What Causes Lump Between Testicles And Anus?

I have had this for years even before being sexually active. I have a lump about pea size between my testicles and anus is have I a white head to it like a wart that would be on your hand. it only comes out during the spring and summer and I have no idea what it is. It usually ends up piping when I play sports or do something active and I gets very painful. And now recently another one has formed a little smaller and I afraid it might be cancer or something. Can you help me.