What Causes Fainting, Dizziness And Nausea?

I have been feeling kind of weird lately. Two days ago I fainted out of nowhere after I got really dizzy and every time I lay on my belly I feel nauseaous... I am so exhausted as well. Me and my boyfriend have recently been intimate but everytime I take a pregnacy test I'm not pregnant. I have not took a test recently but I was on implanon for 3 years and now I don't think I can conceive because we have been having sex like everyday but I have not got pregnant