K.N.
I recall something about how around your daughter's age is when children develop the realization that mama exists elsewhere, even when see can't see you. I don't think her current behavior has anything to do with your pregnancy. Don't quit your job... This is a normal stage of her socialization and development.
Poked around on a search and found this explanation:
12 to 18 months:
Your toddler has learned that you are a separate entity and that you can leave her. However, she doesn't yet grasp the reliability of your coming back, which can make her very upset to see you go. This separation anxiety, which can come and go throughout the toddler years, typically peaks around 18 months and fades altogether by age 3.
In the meantime, resist the urge to sneak away when your toddler's back is turned — when you leave her at daycare, for example. It won't help her cope, and it may just make her more afraid that you aren't coming back.