They cant really fire you. Maybe you could let your boss know that your are pregnant. Chances are they might already have worked it out. But maybe you could let them know, just so they know whats going on and to be understanding of your situation.

I had horrible sickness too. I just sat at my desk at ate arrowroot bickies and drank camomile tea all day, and every hour or so rushed to the bathroom to spew!

I was really vague for a few weeks as well, but that passed. Then it came back in the last few weeks of my pregnancy.

Hope you feel better soon.