What Causes Nausea And Headache Inspite Of Being On Birth Control Shots?

I'm on a birth control shot and I believe im pregnant. I have been feeling very different every time I eat I feel like I want to throw up I've been having headaches everyday and when I came on my period it was light but lasted 9 days and that's not normal for me. I haven't took a pregnancy test yet but I go to the doctor next month. Do you think I'm pregnant?