That sounds AWFUL!
You have so much on (young, very cute baby and being prgenant again), that you want things to be "smooth" at work...
Is it possible that your Line Manager could have avoided lengthy introductions between the new Department Manager and you because you were on the phone? Just asking - sometimes (if people are feeling tired) they can take things out of context.
Do you have any friends at work? Are there people you can talk to and have fun with? Go out and have lunch with? Sounds like you need some support at work... Especially if you have a rough morning - you want to be able to go off to a meeting room (or somewhere) and bend someone's ear...
Regarding the new Department Manager, if I was you, I would put a brave face on it (although I probably wouldn't feel like it!) and go and find him tomorrow, introduce yourself ("Hi, I am Gemma. We didn't get a chance to chat much yesterday when you were going around the office, so I thought that I would come and introduce myself again and have a chat"...). That would make a great impression on him/her and sounds like it would be worth having this new person on side...
If you feel that you are being bullied at work, you need to get it addressed. In normal circumstances, I would suggest maybe looking for another job... but, obviously, you need to stay there for maternity leave...
The best thing to to try to address these things calmly and detachedly - I know that is hard, but it makes your complaints/problems that much more credible... Ideally arrange a meeting with your Line Manager to talk this through: just lay things (unemotionally) on the table, get things straightened out and plan a way forward. If you can't do that (because your relationship with him/her is so bad), then you need to either have a meeting with the next manager up the food chain (i.e. your Line Manager's superior) - that may be difficult and may stress your relationship with your Line Manager more - or someone in your personnel department (these may be easier, they are likely to be more relaxed...).
An "informal chat" with the Personnel Department MAY be the way to go anyway... Pregnant women have rights and EVERYBODY has the right NOT to be bullied - Personnel SHOULD take your concerns/complaints/worries very seriously... They may be able to suggest the best way to proceed in your case and in relation to your company.
You definitely need to get the situation addressed (whether people are bullying you intentionally or, in their ignorance, they are intentionally bullying you and making your life unpleasant) - it is important for you, your family and your unborn baby that you are happy
In the mean time, try to think about the really good things in your life (just to keep yourself happy): you have the cutest baby (love the photo in your signature), a husband ('fraid have no idea if he is cute too!) and lots of other great things I am sure...
Wishing you very good luck and let us know how you get on.
Boo