What Would Cause Pain In My Left Hand Between My

What would cause pain in my left hand between my thumb and pointer finger but close to my wrist? It's been swelling up for no reason like a big lump on my hand and only does it about once or twice a month. I have alot of other symptoms too but I'm trying to keep this short

sorry i cant pay even $15 i raise my 4 kids by myself on $1200 a month