Odd solid lump

So I 19M was just doing a self examination and felt a solid lump, I start to panic a bit but after a while of feeling it it seems to have just gone away. I oddly push my ball right up against the skin (on the inside) and shined a flashlight at it and saw what looked to be a white lump. It didn’t seem to move much and just vanished. Any help would be nice as I’m joining the USMC in like 11 days