well im 18 and every now and then i will have these periods where i wake up in the morning, and when i try to move my lower/mid back will instantly experience EXTREME pain to a point that i cant move until the pain subsides (usually 5-15 min).
then for days after i will keep getting it.
it usually gets less and less painful through out the time i have it. and throughout the day i will have trouble lifting things, even very small things, especially if i hold them out in front.
ive talked to a few other people and i know at least 3 other guys my age that this has happened to.
I'm sorry you're having to endure back pain at such a young age. Since this has been going on for a while, I think it's time to see a doctor. (Not a chiropractor, unless your doctor clears you for that first. A chiropractor can cause permanent damage if he tries to adjust a back with a serious problem.) You can start with your family doctor. He can do an initial exam and order some basic tests. He'll refer you on to a specialist if it's appropriate.
Do you lift? My first thought was perhaps you overdid it and need to give it a break for a while. Either way, it's best to get a professional opinion at this point.
Pain that you are describing could be caused by an electrolyte imbalance, dehydration, and/or medication side effects...I'm sure there are more causes but these are some of the things I've had personal experience with.
You might want to make sure you eat a well balanced diet, drink plenty of fluids, and forgo any unnecessary medication to see if that helps.
18 is very young for back pain, so I know it's not fun to hear from all of us that what you're experiencing isn't normal; but it is the truth. You should definitely make an appointment with your family doctor and let him guide you from there - chances are you'll end up seeing an Orthopedic Doctor.
There could be nothing wrong or something wrong - the earlier you find out the better. Good luck!
"If you can find a path with no obstacles, it probably doesn't lead anywhere.” - Frank A Clark