Pain when aroused

So every now and then when i get aroused it's painful? Touching myself doesn't hurt at all and everything looks right down there. It only happens sometimes and it'll go away after awhile but it feels like a muscle or something? I don't know how to describe it. It usually goes away after I've continued to play with myself. I don't finger myself so it's not because of something like that. Just confused as to why this is happening