I understand your frustrations with the doctors. Someone should sit down and explain it. It sounds like you are really fed up with your body and that is understandable. You should mention to your pain doc that you did not understand the previous explanation and if he doesn't mind would he do it again?
I am not sure if I can explain your report adequately, but I will try to do what I can. I have similar symptoms and I am yet to have my l-spine mri in 2 weeks, I found it was interesting that they commented on your ovary as I also have a thing going on with my fallopian tube and I was hoping the MRI would show it better than an ultrasound did - but my doctor said it wouldn't show it, but now I hope that it will!
Anyways here goes my attempt:
Here is an explanation of the anatomy, try to visualize this first: Your vertebrae each has a hole in it, basically in the middle. To the front of your body (anterior) towards your belly there are big blocks of bone separated by disks that are sort of like thick jelly in a canvas sac. There is then the hole that your spinal cord runs down, with little holes (intervertebral foramina) on each side that your nerves travel out of your spinal cord (or back in) to your body through. Behind this hole and the nerves and such are little joints, and then you have sorta bony projections coming off. Look up a google image search of a lumbar vertebra to try to imagine this.
Here is my explanation of your MRI results as I would see them if they were mine (note I AM NOT A PROFESSIONAL, do not take what I say to be accurate)
1. Mild multilevel degenerative changes seen in this of a congenitally narrowed canal ---> "congenitally narrowed canal" this means that throughout your lower back there is a permanent narrowing of your spinal canal (where your spinal cord/nerves go) that you have likely had since birth. This means that if you get any irritation or inflammation you may have more symptoms because there is literally likely less "wiggle room" for your spinal cord and nerves. The degenerative changes are normal as we age, especially the fact that it is at all levels (throughout your lower back) - but I suspect that you likely have a bit more than would be normal for a 23 year old, as your spine should be pretty much at its healthiest and strongest around 20. I do not know why this is? But it does mean that the pain you experience is real. There may be pain and/or inflammation associated with degeneration of your bones, disks, and this likely irritates the nerves a bit.
2. Mild superimposed L4-L5 central canal stenosis ---> this basically means in your lower back between your 4th and 5th lumbar vertebrae your spinal canal suddenly narrows. This is listed as mild, so may not be the cause of all of your symptoms - but definitely some. I am not sure why you have stenosis, this seems like it is another thing that you have had since birth. You could look up online something called a "dermatome map" to see where those nerves from L4/L5 run to and look to see if the areas of pain in your legs and sides and back correspond to the L4/L5 disk space.
3. Small disk bulges leading to mild foramen encroachment most pronounced L4-L5. ---> Your disks are bulging towards your back and it is bulging into the area where your spinal canal (nerves) run. This can also cause pain, etc. This is also more pronounced at the area of L4-L5 (also where your spinal cord also narrows). Make sure you look at that dermatome map. It seems like your problems are mostly from this level.
Who ordered your MRI? Do you have an osteopathic specialist? I am not sure if they could do any sort of surgery to increase the space for your spinal canal. You should probably have more investigations and this should definitely be followed as it sounds like you have a history of symptoms, your symptoms sound quite severe and it sounds like they are worsening. I am sorry you feel so awful. Sometimes genetics really suck
It sounds like you did not do anything to cause your pain, it is just a function of how your spine is built and how it is also degenerating a bit. Perhaps your pain doctor can get you on a good antiinflammatory and perhaps a neuropathic pain drug and you could get off of the strong narcotics and still have good pain control. I don't know how tall you are or if you have any weight that you could safely lose - but perhaps if you could lower the stress on your back it will not cause as much pain. It is good that you are seeing a physiotherapist, hopefully they can help you prevent further bulging and degeneration so that you can deal with the congenital problem pain.
4. Small hyperintense focus right ovary likely representing small hemorrhagic cyst. Potentially could represent a small dermoid. ---> This if a hemorrhagic cyst could cause pain near your ovary. Do you have a gynecologist? Have you ever had a pelvic ultrasound? Are your cycles regular? Are you on the pill? If it is a hemmorhagic cyst it is the most common type of cyst. Sometimes they can cause additional problems such as clotting or rupture, but yours is noted to be small so hopefully it will do what most do and slowly get absorbed and go away. They also mention it could also possibly be a dermoid cyst. Dermoid cysts are weird - they are collections of mature skin cells and sweat and hair follicles. These are usually benign because the tissue is mature. I would suggest that you ask your GP or gynecologist to send you for a transvaginal pelvic ultrasound to better evaluate what is going on with your ovary.
I would hope that you get an orthopedic consult about your MRI, especially whether anything can be done about the congenital stenosis and narrowing. I definitely believe that all of your symptoms are real and I believe that this MRI proves it. It would be good to find out if the degenerative changes are anything - perhaps you could ask to be evaluated for degenerative spinal conditions such as ankylosing spondylitis. They may do some bloodwork as well such as a CBC, ESR, C-reactive protein, HLA-B27 antigen, rheumatoid factor, etc.
I hope that you find one of your doctors to really help you do what you need to do to feel better. It is really not fun at 23 to go through what you have been going through, and it is too bad the doctors seem to be brushing you off and forgetting about you and your story. Hopefully the pain management dr. can help you get your life back
Need Help interpreting results please- Had MRI for Back Pain and possible ovary cyst? 
