In my last pregnancy it was terrible. I was sick after every meal, had to try and constantly eat little bits as a full meal would come out immediately.
I threw up in the classroom once (teacher), thankfully a year 13 class. I swapped classrooms to be near the loo, and had a gap year student with me in all lower classes (taught mainly 6th Form) so I could just run out.
I had to tell my boss a lot earlier than I anticipated (needed the gap year student) but I was determined and it became a routine. Happened about once every working day and once on the way back home in the car (bucket in passenger footspace).
Thinking back now it seems ridiculous, but I was fine otherwise and after throwing up I was ok.
Lasted 18 weeks, after that I was only nauseous for another 10 weeks, until 28 weeks.
I think if i'd gone to the doc I would have been signed off, I lost a stone in the first 18 weeks. I gained it all again, and baby was 10'4 
I couldn't let my Sixth Formers down and I could not face being at home and feeling sick anyway.
Do whatever gets you through the day.