I've gone through the same thing, but you have nothing to worry about. I'm very sexuallay active, and I've had many scares like this! periods are very bipolar. the more you have sex , the more likely your pH levels drop. I use summers Eve body wash to Ballance my pH. I also take iron supplements. this is a very easy fix. there isnt anything abnormal going on and you shouldn't be worried. I was having sex everytime I was with my boyfriend (every other day) and missed many periods your body doesn't have enough pH discharge to push out your period, just take thoes supplements and you will be good to go. ive experienced everything you're going through. if you have anymore questions let me know. (: