Emotional almost 3 yr old & pregnancy

We and daycare have noticed she is very emotional lately, tantrums or stand off-ish. I keep telling them I think it’s the pregnancy, maybe combo’d with just her age and growing pain stuff. Plus we just came off a week family vacation so adjusting back to daycare has got to be difficult. Am I making too many excuses, could something else be going on? What can I do to try to reassure such a little kid about the pregnancy and new sibling coming? She’s pretty verbal but I don’t know if it’s all really getting through to her.