I Have A Blister In The Roof Of My Mouth

I have a blister in the roof of my mouth right at where my two front teeth meet at the point on the roof that has been there about a week. At first I thought I had just scratched it but when it didn't heal, I finally looked at it and saw it was a blister. At the same time I have a small blister on my bottom lip, in the front, but not on the outside like a fever blister but just inside my lip. It has also been there about a week. The blister in my mouth is sore but the one on my lip is mainly a nuisance. Also, I have never had a fever blister. I just felt like it was strange that I had both of these at the same time.
I have RA and am currently taking Arava, Prednisone, & Methitrexate as treatment for that.
I know that's not much to go on but I haven't had anything new since the doc added the Meth. (about 3 months).
Thanks.