Lamictal - ineffective after awhile?

I've been on Lamictal for about two months now. I started at 25mg and have slowly worked my way up to 200mg. It worked amazingly well for the first month or so, but then my pain started to come back more aggressive than before. I've been on 200mg for a few days and feel some reduced pain, but it could just be that I'm having a few good days. Has anyone else used this and had it work, then had it become ineffective?