You sound like work is really is starting to take its toll on you.

I don't think that there is a certain period of time that you should work up to. Each woman's body responds differently to pg. Some women suffer extreme m/s and exhaustion while others do not seem as affected by it.

The most important thing for you to do is to listen to your body - if it is telling you it is time to cut back on your workload then that is what you should do. Whether that means going to p/time or finishing up at work all together, you have to think of what is best for you and your bub.