Cheer up! It seems to me that you have very unaccepting friends.
I have a good friend who very often will go MIA on me even on the very day we were suppose to meet and her reasons would be that she’s caught up with work and have unexpected OT every time. I admit I do get frustrated when she stood up on me many times but I believe trust and understanding are very essential in maintaining good and lasting friendships.
Trust me if you were my friend and before you tried to explain why you couldn’t make it to my birthday, I will be more worried if you are undergoing any difficult situation hence couldn’t make it than upset of your absence.
My advice will be just move on because you have tried your best in salvaging this friendship yet they just don’t appreciate you. In my view, you didn’t lose them- they are the one losing you.
Be strong, get more rest and enjoy ur pregnancy !