I have not had a period since early October. I went to the doctor and they said that it is because i am more active than I used to be. But, I know something is going on because I am not myself any more. I go to the bathroom like every 10 -15 min (way more often than normal). By breasts hurt alot and my nipples are always hard (which only happens when I am cold). I have also had alot of nausia and vomiting in the morning, also I am cold all the time. What is wrong with me.

you are probably pregnant..have you taken a pregnancy test? You probably should take a test and then confirm with your dr.
Good Luck!