I'm 19yrs old and I have a hard foreskin it doesnt slip much down. Do I need a circumscision? I mean will it affect sex or pain during sex?

Here are some ... Clinically, you would be probably okay with what you have because you have seemed free of the adverse effects from "hard foreskin"; but, it's hard to advise if you need circumcision without a direct look. So, see a urologist timely to decide how to correct your problem as needed.
Hard to say. An evaluation by a urologist would provide enough direct information for you to make this determination. A full circumcision may not be necessary to solve your problem. Either way, the best answers for your question require a more direct evaluation.