I am having the same problems you are! I am also pregnant and having a horrible time. I go to the Heart doctor next week. I was told last week I have Tachycardia which I still do not understand. All I know is that I have NO ENERGY, I can't catch my breath & that fast heartbeat that tends to be worse when I walk & sleep?? Maybe we can keep in touch and help each other out. I hope you get to feeling better!
A resting HR of 132 is too high, but not dangerous in and of itself to my understanding. That seems to be what your doctor also thinks. I'm not sure what pregnancy plays in heart rhythm issues, but someone of this community who has been pregnant and had heart rhythm issues may respond to your post.
That Holter (I think that is the "name" used here in the USA for short-term heart monitors that are wore for 24 hours or a bit more) may be able to catch any irregular activity as well as get an accurate record of you HR.
The B12 deficiency may also contribute, I do not know and haven't tried to verify, this too may be responded to by someone who has a personal experience they can share.
Overall, you are under a doctor's care and while I think they need to find a way to lower your rest HR, I think you really have nothing to worry about. Just be a calm as you can and work with your doctor(s) to find the best path forward.
Good luck with your HR and with your delivery of a healthy baby.