I Am Experiencing Significant Pain In The Lower Part Of

I am experiencing significant pain in the lower part of my left thumb. I am right handed and don't remember doing anything to my left thumb. I woke up with the pain on Saturday by Sunday it was much better and on Sunday it was gone. Just a few minutes ago I was putting a lid on a tin I keep my cat food in and it came back in a big time ouchy way. Do you have any idea what this could be. I am not a gamer, I',m 70. I don't have arthritis in my hands. But it really hurts.