Ive had numerous mc and made up all sorts of excuses.

Once I said I had a bad flu when i had to take 2 weeks. That lie was hard to maintain though.

Another time I said I had to have a minor day surgery procedure (which was true - d&c) and needed a few days to recover. That worked as most people didn't ask anything further and if they did I just said its nothing serious just something I had to get fixed up and left it at that.

Another time I blamed a gastro bug...

At the end of the day it's up to you and how close you are with your work colleagues. I didn't want mine knowing we were ttc as it might impact on my opportunities at work.