What Is The Cause Of Nausea And Lightheadedness?

i need advice im not sure whats wrong with me but teh past two months ive beeen feeling nausus in the mornings when i eat or think of eating i have got light headed my pioreds still come but there lighter or heaveyer .. im on bc .. and have sex regualry i dont what to think my breast are always tender but when i take a preg test is neg