Too soon to test? Signs?

So about a month ago I had sex on my period and he ended up cumming inside of me. I don't know how likely it is to get pregnant while on your period but my period after that was sort of weird and just sort of spotted and stopped. Now every so often I get nauseous, and I have been having lower back cramps/aches. I also have be exhausted lately and starving lately no matter how much I eat it seem like I'm starving 30 minutes later. I took a test a couple days ago that came out negative but I still have about a week until my period starts. Is it too early for a test? Any advice?