I go through phases of paranoia, especially social anxiety as it pertains to what people think about me. If it's really severe for you then it's good you're seeking treatment, but there are also things you can do to work on your thought processes. I highly recommend keeping a journal and putting your thoughts on paper. Sometimes seeing them in writing and reading them back to yourself can help you get a better perspective and see the obsessive thoughts more clearly for what they are. Meditation is also good for me, I'm not good at sitting quietly with myself but moving meditations like yoga or breathing exercises are a good way for me to re-center myself and watch my thoughts like they are separate from myself rather than a part of me. Another trick I've learned that has been helpful is if I feel like someone has slighted me or doesn't like me, I will wait 23 days before I act on the feelings. If I still feel that way after 23 days, then I'll bring it up with the person I feel bothered about. I put it on my calendar so that I can tell my obsessive thoughts I have a plan for dealing with it. Any time it starts to bother me, I look at my calendar and tell myself "this is the day we deal with this". It helps to keep my obsession under control, and most of the time the feeling has passed well before the date on my calendar. If it hasn't by then, there's a better chance that my feelings have some basis in reality.

Good luck, I hope you are able to find some relief soon!