End Birth Control Early?

bells
So I went to see my lady doctor today and she prescribed me birth control to regulate my periods. 
My question is, if I start the pill today, like my doctor told me to, can I just take it for two weeks and stop the pill so my period will come on the original date it's suppose to (around the 9th) ? Then start another pack when my periods over? Or do I have to finish all 21 pills?
I've been on the pill before, but I've always started on the 5th day of my period. I asked my lady doctor and she said just to start today, sobIm just wondering.
Thank you!