confused and worried

I've been feeling super nauseous lately and dizzy every now and again...I had protected sex on September 7th and I go my regular period last Friday, and it ended yesterday. I know everyone says it's not, but could it be possible to have your period and still be...pregnant? Though I took a test yesterday in the afternoon and it was negative. Otherwise, I don't know what to do about this constant nausea, it's completely ruining my life and it's such a bother. 😔 I guess I'm just looking for some piece of mind, or advice on how to reduce this discomfort. I also don't have a fever so i don't know if that makes a difference.