OCD can be heredity and we have lots of OCD in our family.
We have discovered we have inattentive ADHD too - its more common in women with OCD then I think people realise. Inattentive ADHD is busy mind rather than busy body and it feeds into the OCD because your mind is running a hundred miles an hour and you don't register information so naturally recheck stuff.
I used to be a big checker but don't really do that anymore - if I am getting stressed and noticed I am checking things I either say out loud or in my head 'I have checked X' so it helps me remember I have done that.
My son's way of mostly knocking his OCD on the head was to think of the worst thing that could happen and then accept it happening. ie you are worried your cat will die - you've had it checked with the vets twice now and as an animal its going to get its needs satisfied with or without you - so if you really want to stop worrying about the cat you are going to have to say to yourself I am not going to worry about the cat anymore, and if it dies, it dies.
I also suspect you are not breathing properly - when we get stressed we start doing chest breathing rather than belly breathing and so you are not getting enough oxygen to your brain and hence its not thinking clearly.
Try some breathing techniques to ground yourself.
My daughter has the OCD where she constantly seeks reassurance from me - is very difficult for us both. The psychiatrist explained with behavioural OCD you have the process of the thought and then the behaviour so more chance of stopping the behaviour. With compulsive thoughts there is less time to stop the action of asking the question.
Fundamentally, OCD is really our response to anxiety. Other anxious people bite their nails or have panic attacks or whatever. We have compulsions to try and reduce our stress/anxiety - what we have ended up doing with my daughter is she has stopped 'OCD' specific therapy and focuses on learning to deal with her anxiety.
When my children first developed OCD the therapist said to me that my mother (who has anxiety and OCD) was never taught the tools to manage her anxiety as a child and therefore did not teach me, and in turn I did not teach my children. If you feel you did not learn how to manage stress/anxiety as a child then focus on learning these skills now.