oh Haycal, I feel for you. It's impressive what scary images ones brain can conjure up, usually a lot more frightening than reality.
As you pregnant you definitely shouldn't be taking any meds but I do however think you should go back to your GP and ask to be referred to a therapist. You need someone who you can voice your fears to and who can rationalise your fear for you. I know you spoken to your mum but speaking to a therapist will give you tools to work with. In the meantime would it worth getting an alarm system installed in your mum's house that is rigged up so that if the alarm sounds the police is notified? Would that put your mind at rest a bit?
When you think of someone breaking in, what do you think of? Burglars rarely attack people and if disturbed they will make a run for it. If someone was to break into your mum's house, I doubt very much that you would get hurt by it. But is it the intrusion you're thinking off?
Don't carry this around with you, as you mention, it probably won't do the pregnancy any favours. Look after yourself and remember there are lots of people on here who will listen