Hi ladies! Sorry I've been MIA, I had the stomach flu this week and it was absolutely horrible.
First - It is your boyfriend's ex. He should be the one dealing with her, not you. He should call her up and yell, scream, threaten a restraining order, whatever he needs to do to get her out of your life. You don't need the stress with the baby. It's not good for you or LO. She's obviously not responding to you except to take a different approach when you start calling. Maybe a call to the police saying this woman is harassing you and then they will call her to get her side of the story would show her that you are not messing around.
DO NOT go over to her house because if it ends in a fight YOU will be the instigator for showing up over there. And there's nothing good about a pregnant woman who is in handcuffs. Plus if she can get you arrested for trespassing, harassment, or assault, it will just tickle her pink.
Your OH really needs to take charge on this and if he can't see that this stress is causing harm to his unborn child and or is unwilling to do anything about it just to protect his ex of 20 year's ago's feelings, I would begin to worry about what his true feelings towards her are.
I've been cheated on and I've cheated on someone before. And I can tell you that if your OH is willing to stand up for their "friend/ex/whatever" over your feelings (especially while carrying their child) when it is something totally legit, then something is going on. So you need to make it clear to him that he needs to resolve this and anything less than her severing all communication to your immediate family is unacceptable.