Hi. I Am Currently Experiencing Cold/flu Symptoms. Also My Period

Hi. I am currently experiencing cold/flu symptoms. Also my period is late, I'm on cd 36. I've never been this late before, only when I was pregnant. I don't believe I could be pregnant, last time had unprotected sex was 12/24 and I received my period 1/9 and recent tests show negative. I have a slight fever, headaches, diarrhea, dizziness, and runny nose. I rarely get sick, am in good shape, and my diet has not changed. Please help in identifying what could be the cause. Thank you!