Short period

So my period only lasted one day & I had really bad cramps and nausea and the day after I started getting a really bad fever, headaches and I was so exhausted. I did some research and the closest i could find to what was going on was "successful implantation" . But I've never had unprotected sex. So there's kind of no way. I'm not really sure what to do. I'm really worried about it..