You're not eating enough. You're not training heavy enough. You're not lounging around enough.
Read Dan John's "Big 5 of Getting Big" here on T-nation.
If you want muscle and strength, guess what? You're gonna put on fat. Otherwise, progress will be slow and frustrating. You are 17 years old. You are far too skinny to be doing any more losing weight.
Lots of PR's and strength/muscle come from a McDonalds bag. Just don't go crazy with it. Getting big is a cycle.
I read about and talk with guys like you often and they all tell me they eat a lot. But if that's the case, why aren't you gaining weight? Nothing worse than training your butt off and nothing to show for it because you're afraid to lose your abs........which is their problem with trying to make progress not saying its your issue.
Fact is: you gotta eat big to get big.