I have very painful urination and urge to urinate frequently. what would be the reason for that?

The most common cause is lower urinary tract infection (cystitis = bladder infection). You need to drink a lot of fluid next couple days (5 x 500 cc bottle) and try Azo OTC (phenazopyridine) for a day or two. If symptoms do not improve next day, you should see a health practitioner for urine check and antibiotic. If symptoms improve next day you continue with hydration for a couple days.

Agree with Dr. Le that the most likely cause is a urinary tract infection, possibly cystitis. Your doctor can obtain a urinalysis, and culture and sensitivity. If proven presence of bacterial infection, treatment with antibiotics will reverse your problems. In the meantime, increase your liquid ingestion.