Does being skinny affect you period?

I am 19 years old and I am ually active (I weigh approximately 110 pounds). I do not take any sort of birth control, either. I have very irregular periods ranging from 25 days in a cycle to 40 days. This past period cycle lasted 40 days and I bled for 8 days. Two periods before this one I was all hot and sweaty the entire time. Could this be a sign of early menopause? I also had to take the Plan B pill midway through this past period (5 days ago) and I have noticed that I am constantly eating more than usual (but not craving anything). I also had a very bad headache today (the first day I stopped bleeding), and I noticed I have been a little gy lately. Is there something wrong with me, or is this just a side effect of the pill? I've never taken it before.