Missed period?!

I've never missed a period since ive started, but this month I'm 8 days late. I've taken two tests and both came back negative. I had unprotected sex just over 2 weeks ago, not thinking anything of it as I had stopped taking the pill a couple weeks before and thought I'd still be covered by it, am feeling sick every morning and evening, getting stomach cramps and am so tired every day, if my pregnancy tests are negative could there be anything else to worry about?