It wasn't Lyrica with me- it was Neurontin. I didn't gain 20 lbs. in a week but I did seem to start gaining OVER NIGHT with it- I mean, almost immediately.
Alot of these kinds of meds are known for having that as a side effect. All told, I gained about 30 lbs. very quickly and even though I'm not taking Neurtontin right now, I still can't get rid of the weight. You definitely need to talk to your doctor about this though, just to make sure that there isn't something else going on.