What Are The Side Effects Of Using Emergency Contraceptive Pills?

im 16 125lbs n 5.5 i am on birthcontrol i have neen on it for a year. i started a new pack a little over 3 weeks ago and i started to bleed 2 and a half weeks ago still am too.. i am sexually active also it isnt like a period though. its more like i would be ending my period its like a dark brownish color at first then it went to pinkish red then red now it is back to pinkish red i dont know whats a matter with me! and i am suppose to start my period this weekend. also i have been having pains around my bikini line and my lower back.