I used to get infections a lot at your age. Finally had a gyn tell me that after my ride, get into the shower ASAP & wash with mild soap. Then dry the entire area with a hairdryer (big hint - use the cool shot button! ). You might have to put one foot on the sink to get at everything - I mean really really dry. Then put on some loose shorts & go commando (without underwear) as long as you can.

Works for me.