Any ideas please

I had gotten off of my period Sunday of last week, then had sex Wednesday of last week also. He did not cum in me but did precum. I have been having symptoms like bad back pain, some nausea, spotting (dark brown) just noticed it once, bloating, headaches, super fatigued, I have also been super hungry too. I am on birth control and never have had an issue. I have also taken two pregnancy test and both have been negative. I'm so confused. Any ideas on what is going on or if I could be pregnant?