Re: back pain
Many people gain quite a bit of weight on gabapentin. It seems to increase appetite, and then, as everyone said, with the pain it is difficult to get much exercise.
I would suggest you eat some protein with every meal or snack, and drink lots of water. It is good for the discs as well as the appetite.
Know you are not alone in this struggle. When you have back pain, it is really difficult to avoid gaining weight.