Why do I have a hump in my penis?

I am a boy and I am using this profile so I can stay anonomas. I am a 13 year old boy just learned how to *** 3 days ago. I have been doing it every night. This last night I was really jacking off and an hour later had a hump in my penis. It is kinda painful and I have a ring around my penis. I did it with a girl when I was 11, could I have STD or aids? Please help!