Sores on side of tongue. What the hell?

I keep getting painful sores on the side of my tongue. It's not thrush, as there is no discoloration or bad taste. I had these sometimes (but seldomly) before I was pregnant, and it was usually a vitamin deficiency. I'd take a vitamin and in just a day or so, they were gone. But now I'm taking my prenatals twice a day every day. Is it possible most of it is going to the baby and causing this? I want him getting all the vitamin-y goodness, but sheesh these hurt! Anyone else experiencing this?