I haven't taken lyrica, but do take gabapentin (a similar drug). I do have a theory on the weight gain issue, based on my experience with gabapentin.

Your body has two "hunger signals" - one that signals you to eat when your stomach is empty, and one that signals you to stop eating once your full. For me, I don't have any major cravings that push me to start eating. However, once I start eating, I have a really hard time stopping. (Gabapentin seems to prevent the "stop eating" signal from getting through.) I might decide to eat a small sandwich for lunch even though I'm not super hungry. But after I finish the sandwich, it takes a great deal of effort to prevent myself from following that with a whole bag of chips and a dozen cookies for dessert.

I was on gabapentin in the past (for something other than PN), and went from about 190 lb to 230 lb in a year. I was able to lose that weight after quitting the gabapentin. After my PN symptoms, I went back on the gabapentin, but this time I'm aware of the weight gain issue and have only put on a few pounds. I have made a decision to never go back over 200, and although its not easy, I'm so far managing to meet that goal.