Pregnant or just sick?

Me and my husband had unprotected sex 2 weeks ago, my period ended 3 days prior to that. This past week and a half I have been so nauseous and have had the worst headache. I have never felt like this in my life. I have been in bed all week with the blind covered because the light just makes it worse. I keep testing but the tests are negative. Is it possible I'm pregnant, but it's to early to pick up on a test? I also had slight bleeding a few days ago but my period isn't supposed to come for another two weeks. Could that be implantation bleeding? I know all this is possible but am looking for someone who may have a similar experience or if it just seems like I am sick, but still I have never been sick like this before with only nausea.