Hemorrhoid or fissure, help?

Okay, I was in the using the bathroom, and I believe I was constipated, or it was just hard stool, but It felt like it cut or tore some of my colon or whatever it's called and there was a smudge of blood on it. I've had a fairly bad diet, eating quit a bit of fast food, i'm not over weight at all, I'm fairly slender, just have been eating a lot of greasy foods recently, I'm 17 years old. Is this a fissure or a hemerrhoid? Do I need medical help? (As it's not very bad, just hurt at the time)

Also, before I forget, I was in the weight room for P.E today and I used the Leg Extension machine, I pushed 250, which is quite alot for me, and it used alot of strength/straining.

Any help is appreciated, No trolling for god sake.