Been there a few times, in the initial period it’s easier to gain reassurance by looking at sources on these thoughts and research into OCD that may provide a short term fix but as a long term sufferer of OCD my best advice would be to channel your energy into something hobby exercise etc and essentially diver your energy. If it’s at a really critical stage where you’re in a state of panic then you need medication treatment initially. Also essential that you find ways to relax where possible