When is the soonest you can start gaining weight/stretch marks???

Is it possible for your boyfriend to have morning sickness for you?/with you?

Hey! I'm new on here, but I was wondering if anyone could help me?? My period is over 3 weeks late, and I spotted for one day about a week or so ago...and still since then my period hasn't come.. I've taken 3 pregnancy tests but all have come out negative..why? Does anyone know?? Am I pregnant or not? And if I am why are they coming out negative??