onebeed -
here is a pretty good article outlining the possible reasons Lyrica causes weight gain most of them still have to do with changes in diet and exercise after starting the medication (like less exercise because the drug makes you sleepy or an increase in appetite). Also weight gain only affects between 10 and 20 % of people and most see the change over a long term of treatment

http://mentalhealthdaily.com/2015/02...ld-you-expect/

I was reading through comments and a few people were claiming lyrica made them gain like 40 lbs in one month or 20lbs in a few weeks and I have to believe that there is no way this happened without some change in their diets or lifestyles in addition to the medication because this is drastic. If I were you I would monitor your weight each week to see what happens and try to maintain a healthy lifestyle so that if you do gain weight you can be sure it is the medication causing it. Hope the article helps!