Depo Provera

I was on Depo Provera (the Depo shot) for 3 years and my last shot was August 2013. Earlier this year my periods started going back to normal about the time I got with my new boyfriend and we have only use condoms half the time we have sex the other times he pulls out. Well about 1.5-2 weeks ago I started feeling nauseous a lot and had various other pregnancy symptoms but last week when I went to the hospital they said I wasn't pregnant. Should I still worry about being pregnant? I also have had a stomach hernia that will always be there that can make me sick but doesn't affect other things like mood changes and cravings.