I don't know the answer to your question but I know I suffered severe paranoia at one point during this illness. Ended up getting my antipsychotic increased and it took care of the problem.
I'm sorry you are having that problem, yes it's common. Just another wonderful symptom.
I have that really bad, totally paranoid about something happening to my husband. Every single day I get horrible thoughts/vision of him dying in a car accident. It's awful. Also, I am kinda paranoid about people talking about me behind my back; I always have been mostly because they were! But it's like, every time I go out of the house, I think people are staring at me. I hate that.
I haven't found anything to get rid of these, but Laura is right, antipsychotics do help a little. I take Seroquel, no weight gain on that one. Careful about your diabetes, tho. They can all make it a little worse, keep an eye on it, you will be ok.