Im 19 and I've been w the same guy for 6 years and we've been trying to have a baby for 3 yrs I really don't know what to do?!

First I would consider serious counseling, since anyone who wanted to start having children at 16 has issues.

Beyond my moral opinion, have you both went to the doctor for a physcial exam?
Are you properly tracking your ovulation period ( not a phone app or online tracking) but real medical tracking

Only then can issues be determined

I agree with Chuck. You are actually very lucky you haven't become pregnant yet.

But what you do is talk to your Ob/Gyn and discuss the situation.