we have to say Positive phrases when we start to think those scary ones so each time you think something negative replace it with a positive statement and they don't have to be really long statements.
Please do not follow this advice! This will make your symptoms escalate in the long run.
OCD has suckered all of us into believing that our thoughts have power or meaning just because they came from our own mind. Trying to counteract a thought with another thought is just feeding that incorrect belief. The thoughts themselves are not
the problem. The real problem is our reaction
The reality is that you will never be able to think yourself out of OCD. You will never be satisfied by any thought you force your mind to conjure up to counter a bad one. Absolute certainty is impossible to have and yet we fool ourselves into thinking that if 'I can just be sure that xxxx', everything will be fine. Completely false.
To answer your original question... Yes, OCD will make you doubt everything and I do mean everything. It will always attach itself to whatever scenario is your personal worse case scenario, which, for many, comes in the form of 'what if I am not the person I thought I was?'.
Our thoughts do not represent reality. They are just simply thoughts. They are just chemical reactions, not prophecy, not judgement, not indictments.