I Went Up To The Mountains Two Weeks Ago Wednesday.

I went up to the mountains two weeks ago Wednesday. Everything was fine, I was supposed to get my period that day but it came on Thursday. Still everything was fine, I felt ok. Then I went to the bathroom (to move my bowels). Everything went well until afterward, I suddenly got very nauseous and then for the next fifteen and a half hours I threw up bile. I had the chills and really bad sweats. No fever but temp dropped to 96.5. I usually run warm, 101 is a low grade fever for me. I noticed my period was light pink and like water but everything that came out of me that day was water. The next day I fidnt throw up, was over exhausted and my period was normal. Then the next day it was just very scanty spotting for three days, then nothing. I have had a headache everyday since. Then today I went on the swings with my seven year old step daughter and every time I went up and came down I felt my stomach drop as though I was on a big roller coaster ride. I love the swings and have to be going really high in order for this to happen. I have taken two pregnancy tests but the one from today was in the middle of the day but both say negative. What can this be? Could I be pregnant and just not reading it on the tests? Could it be just random these things all coincided together and that’s why everything got all messed up? Or could there be something else?