What Causes Cold,nausea,hot Flashes And Light Periods?

I've been sick for the past week with a cold/sinus cold. For the past three days I've been getting ways of nausea. I think I've had a fever along with this because I've been getting hot and cold flashes. I'm on the birth control pill and get my period every three months. The last time I got my period it was really light, which is unusual for me. I'm 20 years old and am a very active person and I eat a healthy diet. I noticed that my stomach isn't as tight as it usually is. I haven't changed my eating habits or my exercise habits in the last few months..Before my last period I had sex without a condom..is there any explaination for this or do I simply just have a flu bug?