Just engaged and possibly pregnant

My fiancé and I just got engaged at the end of September. And now I think I'm pregnant. I was supposed to start Friday, today is Monday. I've had all sorts of symptoms, including throwing up, sore breasts, ligament cramps, sleep cycle changes. I've had 3 negative pregnancy tests in the last few days. He knows all of this and he think I WANT to be pregant and he doesn't want another kid right now. (He has a 4 year old) I am so upset because he isn't taking me serious. He thinks that just because it's a negative test that I'm not prego. I just need to vent and someone to talk to.