Welcome to the MS board.
There is NO MS test from the spinal fluid. If a doctor relies on the spinal fluid, the doctor is wrong. MSers who have had an LP (not required but recommended) get mixed results. 85% are positive for indicators of a neurogenic problem, BUT 15% are negative- that is their spinal fluid has no O band indicators. I have had MS for nearly 35 years and I have had 2 LP's 20 years apart. Neither LP was positive.
I think that due to the demyelination as indicated in your MRI and your symptoms, you have MS. Unfortunately the nerve pain due to MS rarely responds to meds. My worst MS nerve pain has been in my lower back and left thigh. I treat this pain with a heating pad. The heat seems to shut down the nerves and the pain disappears like melted butter.
For severe pain in my head, I have three different pains. The first one is in my right eye and is linked to light sensitivity. I get relief from this pain with acupressure applied at a point perpendicular to the pain- usually on my temple. The second pain is in the center to back of my head. This I treat with Diet Dr. Pepper (something caffeine it would appear). I have tried other caffeine products, but nothing works as quickly as my Dr. Pepper. My third head pain is in my lower part of my skull. For this one I use dark chocolate. Again, the pain seems to evaporate. The first and last pain sites are not as frequent, but they are still severe when they strike.
As to your pain med- gabapentin. If it is not working, DO NOT quit cold turkey. You need to be weaned off of it to prevent any serious withdrawal reactions.
Lupus is a different disease and would not have demyelination associated with it. IF you have Lupus as well as MS, you need to have two separate specialists to work with you.
Stay strong and I hope you get to feeling better soon. I will add you to my prayers. Also, please feel free to visit here often- you are not alone.