Birth Control

I am a 17 year old girl put on birth control recommended by my doctor. It's used to control my period cycle and help me regulate as I'm off due to being an athlete and other stresses. 
I will have soon finished my first cycle of taking the pills (21 days) and I would like to know what the after results are in the seven days like will I definitely get my period or will it take a couple of times to regulate my cycle?