Was it your normal practitioner or a specialist? "Fighting" it can actually be one of the worst things to do depending on how you do it. If you try and "fight" the thought, specific try and either intentionally forget it or logic it away you often reinforce it because you keep thinking about it. There are definitely ways to approach OCD and manage it, but its tough to do it on your own without atleast some literature because in many ways its contrary to how we would face regular real world problems. If you were to find a description of OCD somewhere and read it, like in an encyclopedia or on a medical site, I imagine you would be amazed at how it applies to what your thinking.

OCD in particular is unwanted thoughts or feelings that you KNOW are illogical but can't seem to stop and make you uncomfortable and anxious. Some people deal with them through compulsions tht provide temporary relief but don't solve the problem in the long term. Sounds to me this is exactly what you are dealing with.

"What if" thoughts happen to just about everyone, unfortunately for people with OCD for whatever reason, there is osmething wrong with our brain chemistry that don't let us "let go" like non-OCD people can. We overeact to anxiety stimuli of certain types. Medication can help regulate it and so can a specific type of therapy clled Cognative/Behavioral Therapy which basically re-trains your brain. There is in fact evidence that over time CBT actually changes HOW your brain reacts physically, helping to aleviate your OCD.

I can't recommend enough trying to get evaluted by someone who specializes in these types of disorders, they will be able to tell you much more and help you set up some effective therapies to manage it.