If you have been consistent with her and used the same dicipline repeateadly (that is what is needed-what you use is not usually the issue, doing it all the time, every time is the issue) then you might consider a psyciatrist, but she is really little for that. Even if you loose it, if you don't give in, then you are fine. We are all only human, just don't give in, ever.
I have kids who needed psychiatry, and the fundamental thing you should look for is if she is miserable, and she really can't change the behavior that makes her miserable, even with clear and consistent reasons to do so (your discipline.) If she continues to use strategies that are not successful, then she may have a processing issue that prevents typical dicipline from being effective. It is a matter of degree and function. Her fit may look the same as one of a typcal 2.5er, but if she does not learn anything or improve, then you have more to think about.
I do have advice for this stage, for both typicals and kids with issues beyond this stage. That is, tell her what you want her to do instead of what to stop doing. It is not as easy as it sounds. Instead of "stop whining" say "use your nice voice" or instead of "don't kick" say "put your feet on the floor." It does work when they are so little that they can't process what you have just said, stop doing what you said, and come up with something more approriate to do, it is just way too many steps. One step commands with an action that they can successfully carry out right away will be very attractive to kids of this age and kids who have processing issues well beyond this age. It helps them be successful, and success breeds success.
If this continues, and you really feel like you are picking your battles well, and being unwaveringly consistent, consult a Developmental Pediatrician, found at children's hosipitals. You will find this kind of evaluation and physician to be much more user friendly for such a young child, and you can rest assured that any issue (be it physical, mental, genetic, neurolgical, etc,etc) will be addressed by a Developmental Pediatrician so you will miss nothing and can walk out the door knowing exactly what is, and isn't going on. This is the gold standard, especially for such a little one.
Good luck, I don't think the pregnancy has much to do with it, either for you, or for her. 2.5 lives in the here and now, and the baby is not here yet, and unless your husband has pregnancy hormones too, you are not alone in your frustration.