This is something to speak to your psychiatrist about. Bipolar can cause paranoia and delusions. You will need a medicine adjustment to deal with this issue. On the mood tracker there are the symptoms paranoia. If you're keeping a mood tracker, make sure you mark that box on days when you've felt like that to show how often it happens.
I'm a very paranoid person. So paranoid, that in my past I've made up things and begin to force myself to believe them. Lame example - "he's cheating on me," etc.
I do believe it's a symptom of bipolar. But it can also be a sort of character flaw imo. So I think the habit can be kicked with some therapy.
I can relate to suspiciousness and paranoia which I believe is a symptom of bipolar. It is one of the most troubling aspects for me, and like cirene I have got ideas into my head and talked about them and believed them as if they were real. It can be very isolating if it is allowed to get out of control, so be sure to keep your pdoc updated on your symptoms.