HELP completely paranoid

So I had sex on the 18th with a condom and then got my period on the 27th. I'm on birth control and I take it religiously and my periods are now lighter than they were off BC. I took a pregnancy test yesterday and today and they were both negative. I just need some reassurance that I'm fine and not actually pregnant. I'm just feeling weird, kinda nausea which is making me think differently.