TeenHealthFX is not able to diagnose you for sure over the Internet; it would take a medical examination by your doctor in order to determine exactly what the problem is. It sounds as if this problem is very painful and we suggest that you make an appointment to see your doctor as soon as possible.
The burning sensation that you are feeling when you urinate can be a sign of an infection somewhere in your urinary track. You are doing the right thing by drinking plenty of water in order to flush out your system. You don't mention if you are sexually active but your symptoms can be a sign of a sexually transmitted disease. As mentioned before, it is recommended that see your doctor who can evaluate you and recommend the best course of treatment.
If you do not have a doctor and live in Northern NJ you can contact the Adolescent/Young Adult Center for Health at 973.889.6350 for an appointment.