Is it where the yarn drapes over your finger to hold tension?
The same thing has happened to me, but now I'm calloused like a bass player and I can't feel a thing, so it should get better. If it gets raw, try some triple antibiotic ointment on it overnight.
I had a sore finger experience just recently when I broke out a set of vintage plastic dpns from my late grandmother's cache. They're really sharp, and I got a raw sore spot on the tip of my finger where I'd brace the needle tip to scooch the loops up. Youch!