Nausea and Vertigo, possible heat exhaustion or preggo?

A few days ago I woke up very dizzy, I work in a hot environment and thought that perhaps it was from dehydration or heat exhaustion. The vertigo has continued and is especially horrible in the morning but I can have frequent bouts of it throughout the day and feel nauseous at random times as well. I did take a pregnancy test and it came out negative. I had my period a few days before the symptoms began. Is it possible that I am pregnant? Oh, and if it helps I am 27 and have no children and have never been pregnant. Thanks!