Hello. I am 18 years old and have very regular periods. In November, my period never showed and I was suddenly getting night sweats. But then it came in December (it was a month late), and the night sweats stopped. This totally freaked me out so I went to the doctors and had tests done (pap smear, blood, urine, and I also had an ultrasound). All the tests came back normal and nothing seemed to be wrong. My period came again in January and all the months up until May, which I skipped again. I'm not stressed and I'm average weight, also I don't over exercise. I'm not on any medication either. I just want to know why my periods are suddenly being so unpredictable when they were previously normal?