What Causes Nausea And Headaches After Pregnancy?

Hi, I ve been having heat flashes, nausea and headaches, nausea after I eat certain things and sometimes just randomly occurs throughout the day, I m 21 years old. I just had a baby in September I breast feed exclusively and have not gotten a period since I ve given birth. My child`s father believes that I could be pregnant again, but since I have not gotten a period for 4 months now I don t know if pregnancy is the cause of these symptoms.