I'm 17 and lately I have been peeing alot and I cant hold it. Why does this happen?

Increased urine. Sudden onset passing more urine could be a sign of urine infection or diabetes, or prostrate infection or certain other hormonal disorders .Please see your doctor.
Possible. Sudden onset of urinary incontinence can be a sign of infection, increased blood glucose or other cause. See you physician for an evaluation. .