Can i start taking birth control pills without waiting for my next period to come?

Yes and No: If you are taking the pills for menstrual cycle control and pregnancy is not something you are considering or worried about, you can start the pills anytime during the normal 28 day cycle. However, if you are taking the pills to avoid a pregnancy, you need to be pretty close to the beginning of the cycle. Day 1 of the cycle is the first day of bleeding. Day 14 is usual time of ovulation.

OCP's: Yes, but only after confirming you're not pregnant. Most physicians will have you wait for your period or have you do a pregnancy test.

Only if not pregnant: Confirm the absence of pregnancy before starting oral contraceptives after mid-cycle. If not pregnant, then "back up" the pill with a barrier contraceptive until the next period arrives. Which may not be until after the last contraceptive pill is taken.