Hi Julie,
I've been taking Lyrica for 3 weeks too, and I haven't had any problems with mouth sores. I switched directly over from gabapentin. I'm not getting any more relief than I was on the gabapentin so I might switch back. My side effects are that I am sleepier with Lyrica, and I constantly want to eat. I hope someone else can help you with the mouth sore issue.
Take care, Missy