I had sex with my boyfriend and a week later I spotted very light pink with slight cramps

Hi all, so I'm 19 and I was on the depo shot last year from March-June and I spotted the whole 3 months after my first shot so I decided to stop taking it and since I've only had one period (Late Dec 2016-Early January 2017) after that one they stopped, anyway fast forward to May 13th I had sex with my boyfriend and a week later on the 19th I spotted for a few hours (very light pink accompanied with slight cramps) and I rarely ate that weekend because I was so nauseous, I had bad headache, my neck and lower back hurt for a few days and I was bloated! So now it's been about 2 weeks since I've had those symptoms and some of them are lingering on and I've taken 2 pregnancy test but they came back negative, however I'm still experiencing the same symptoms I'm so confused am I infertile? Sounds extreme but I honestly have no clue on what to do