The thoughts you're describing are very similar to mine and I was diagnosed with paranoid personality disorder 4 years ago. Then what rubystar mentioned, delusional jealousy, also sound a lot like it and I do recognize myself there too.
I did not know I was paranoid or very much on my guard and jealous before I was diagnosed. I never reflected on it. I thought it was normal and the right way to be/think/react or feel. Since I became aware it's been easier for me to distract or prevent myself from letting the paranoia get out of control. But it is still hard at times. It is especially in a new relationship my problems tend to show the most. That, stress, not enough sleep and alcohol tend to make my problems worse.
It could be PPD but I think the best way to find out is to talk to a psychatrist.
~To conquer oneself is to conquer one's worst enemy~