I had that once, it ended up being a stitch that ended up finally poking thru my belly. First it was that lump thing, then it broke
open and kept draining and wouldn't heal, I went to the dr. and he deadened that area with lydocaine and took a instrument that looked like a knitting tool with hook on end, anyway dsr dug around hurt like hell and him digging around was very unnerving, and sure enough he pulled out stitch sniped it off and healed up, it happened two different times