Pregnancy symptoms can be similar to pms symptoms so it may simply be that your period is about to start. How many periods have you missed? It may be worth going to a doctor or clinic such as planned parenthood and getting a blood test done.

Yes, it is possible for a pregnancy test to come out negative even if you are pregnant. It usually happens if you test too early.

However, like eiri said, symptoms don't mean anything. The symptoms of early pregnancy are the same as symptoms for dozens of other things, so it could be almost anything.