Well, there is a really good gastro bug going around at the moment that makes you feel yuk so hopefully some at work will get it and 'end of story' they will stop asking questions.
I had a similar thing and had to take days off work, I just said I was unwell and going to see the Dr in a week for tests. The tests 'results' took awhile to come back so they stopped asking questions.
Not much you can do as the more you say 'no' the more they don't believe you
All the best on the rest of your pregnancy.