What Causes A Small Lump On Penis Head After Masturbation?

I am 16 years old, 5 ft 9 and around 10 stone. I had unprotected sex 5 months ago and a day after it I had red bumps all over my penis head. Which went away and came back a few times. I don't seem to get them any more, so they are not the problem. Instead I have a small lump on my penis head and I recall the area it appeared in to have been hurt from friction of masturbating. So I stopped masturbating for a week and it dissapeared, and then I masturbated quite frequently and it came back. Now no matter how much I try I can't not masturbate for longer than a few days so it wont dissapear. I am confident this is not genital warts as the lump is not painful, same skin colour and I do not have urine pain or discharge. I am sure this is a lump caused by friction so if you can confirm it is how can I treat it? Can you also confirm this is not genital warts or cancer? I am really worried incase it could be them. Thanks