I have this almost exact issue with my left hand. Happens when I grip something like a bar with my thumb around it. It I don't wrap my thumb around and only grip with my fingers it doesn't hurt. It's always been like this. I never had it checked out but I think the muscles and nerves formed a little weird so pressure on that spot compresses the nerve more and thus causes the pain. If it's a sharp pain when you have it then it is very likely nerve compression. If I go a week or so without working it too much it kind of "resets" and I can use it again. Biggest thing I did to help it was get a pair of workout gloves that have thicker padding in the area. They help a lot. Still can get bad if I overdo it. I have noticed, as I have gone up in weight, that the pain does not trigger on the lower weight I used to do. So there seems to be a link to muscle growth.