It could also be an umbilical hernia. You really need to get this checked out.
Hi, I don't know if you've resolved this issue yet, but if the lump is still there, it could be umbilical endometriosis. An OB/GYN would be able to diagnose this. Does it bleed with your period? It sounds exactly like what I had. Doctors had no clue until I went to the OB/GYN. I finally had to have it removed surgically.