What Should I Do About A Sharp Pain And A Small, Bulging Lump Above My Navel?

Hi I have a bad sharp right above my belly button. It happens sometimes when I stretch my belly, and it seems like a small bulge, but its small. It stops hurting when I push on it and it retreats in a way and only re appears when I play sports. When it does happen it s usually when I stand up straight, and it s very sharp. I do not smoke, and I have no digestive issues except for a very fast metabolism. I am slightly underweight for my age. Please tell me what this is, and what I should do. It s a very small lump, yet it still hurts like it s not. Thanks