I am experiencing painful erections. erections for no reason ?

Peyronie’s Disease?: Sounds like it might be Peyronie’s Disease. There are other possibilities but if it is causing you problems woth seeing your doctor and discussing it. http://www.healthline.com/health/erectile-dysfunction/peyronies-disease

You're a man now: At age 18, you'll get getting 6-20 erections daily for no reason whatever. You should be proud of having a normal body. Especially if you haven't had an ejaculation for a few days, it'll get uncomfortable. It's part of the male experience that happens to all of us. If Dad's a reasonable guy, maybe you can talk with him -- or a coach or a friend.