My job requires me to be outside most of the time

i think you should be frank with your boss about your concerns. however whether pregnant or not, with covid most companies have a more remote workflow to avoid spread of cases. i also do sales work but we no longer meet clients face to face unless there is a serious need to do so (not to do pitching). also highly doubt clients will want to meet sales people in the period!

Your concerns are valid. I would be worried too. It's unkind of your boss to expect you to continue doing so. Do you have anyone else other than this boss whom you can talk to? Or are you able to switch roles within the same company?