i have been feeling really weird lately and need help figuring it out?

I have had a low grade temperature, headaches, nausea, lower back pains, body aches, hot flashes, vomiting and constipation. My doctor said that it was nothing serious so i didnt have to go to the hospital he said it sounded like signs of pregnancy. But i am not pregnant and i know that for a fact. I took a pregnancy test a while ago because i thought i was but i wasnt. I havent had sex since then so that is not possible. But he thinks that i am. I would like to know how that is possible if i am not having sex right now?