I suffer something similar. Reasons: desk job, stature too big for crappy chair. Also having trouble with bed matresses... all that makes my spine beg for help.
I'm trying lots of stuff, but not much of it helps. Exercising is probably the best shot.
Thats both strange and good you noticed it that early at 215 lbs. You should definitely strengthen your back, or better everything else if you plan on gaining more, so don't hesitate going to gym. My favorite exercise in the end of visit was hyperextension (or whatever that called, when you lift your torso and straighten body with your lower back muscles) I might have something really wrong with my back, because this exercise gives kind of a relaxing and blissful feeling after finishing it.
Other things I'd suggest is swimming and also recently I was looking at yoga (for beginners one). Especially that pose when you lay on your belly and then lift torso again to form an L