Missed period.

This may be a bit too much information but I would like some advise. In December I was given the first of a birth control shot that you should get every three months, prior to that I had not been on birth control for about six months and was not sexually active. After those three months I decided to go I the pill starting on the 17th of February. On February 9th and 12th my boyfriend had sex and he came inside both times. I was also spotting at this time. I decided to take a plan B pill the next day, the 13th. Fast forward to this past Tuesday the 11th I stopped taking my birth control, the last of the pack. Today is the 16th and marks a 28 day cycle but I've yet to receive my period. I just took a first response pregnancy test and it quickly showed negative. I'm still worried though because I've been throwing up Late at night/early morning, cramping, my boobs hurt really bad and they are very heavy, also all I want is cherry coke and salty foods. I'm not sure what to make of all this.