I Have A Spot On Finger, That Will Sweel Up

i have a spot on finger, that will sweel up ans when i open it up a clear sticky sustance comes out, this has been doing this for about 5 months, I will get this to a point i think it has healed and then it is back again. I worked a lot outside this spring and i thought it was a splinter, but do not think a splinter anymore, i had used black salve on this several time, but it come back,can you tell me what may have biten me