Why am I having Nausea

So I have been Nauseous for about a week but when night time hits it get soo soo bad like wakes me up out my sleep why is that? Also my period was 5 days late having a lot of light to dark brown discharge.. Then it came only for 4 days it stopped so quickly. I normally go 7 days. I took a test within the 5 days I was late but came back negative. But lately I been so sick. Why is this?