I havent had my periods in 4 mths , what does that mean?

im 17 yrs old, myy last menstrual cycle was februrary 23..i had intercourse around march 4, andd another one on march 14. i was waiting on my periods to come on the 23, it nvr kame.! i tld my moma, she said its prolly frm tht depo shot. bt i was off thm shots july 2010.! so ihad waited fa the april 23 to come, it didnt, i took a pregnancy test, it came out negative. so i was like oh well. then i was like so worried, because of cravings like pickle and an ice cream, vomiting, naueseas, bad headaches and backaches, mood swings..sharp pains in the stomach and private area and plus myy boobs frm time to time., i feel like the sharp pains was kuming frm the veins in my boobs, been tiredd alot, senenstive to the smells..i gained some weight, because the last time i weight i was like abt 118 to 123 lbs, i took another pregnancy test, idk the results because they didnt take the paper.bt im not sure wht it is because my friendd had took tht type of test, and she got pregnant and had a bby, so i asked her whts the results is, it turned out wht i had is postive. my stomach started to get big, but its a lil hard and cant feel anything in there. so when i went to the doctor in early june, she told me im not, and i weight 136 and a half lbs.! i dnt have any dieases or infections. i havealot of vaginal discharges.sometimes its white-ish and yellow-ish.! sometimes i feel like i am but dont knw it. you knw wht i mean? i had spotting for 2 days out of 4 mths.! tht was it.! everytime i stopped thinking abt it, it kept on koming bakk., so i feel like sumthing trying to tell me i need to do sumthing, bt the doctors cant seem to find anything wrong with me. can you help me.?