My lil Dudley had something the size of a very BIG pimple on his stomach after we got back from SC in May. At first i thought it was the head of a tick b/c i picked one off in that area so after about 3 weeks of me picking at it, i took him to the vet....I thought it would be lanced, but ended up getting it cut out and 2 stitches later.....it was a piece of "embedded plant material"
I hope it turns out to be that simple for you!