If you are not sexually active, then you are right that that eliminates the possibility of a sexually transmitted infection, which would be one major concern.
That means that the most likely possibility is a urinary tract infection
. Urinary tract infections occur when bacteria migrate up the urethra (the tube that connects the bladder to the outside) into the bladder. Symptoms of a urinary tract infection include burning with urination, blood in the urine, and a cramping feeling before and during urination. You may also feel that you have to urinate frequently but, when you do urinate, feel that you haven't completely emptied the bladder.
Urinary tract infections are very common in young, otherwise healthy women. In fact many young women will have 1 or 2 urinary tract infections each year, and this does not necessarily mean that there is a serious underlying problem.
I would suggest that you go see your primary care doctor
or your OB GYN doctor. They will be able to perform some simple urine tests to confirm the diagnosis of a urinary tract infection. If an infection is diagnosed, they will give you a prescription for antibiotics, which should be able to clear the problem up quickly.