Hi Emz,
The irrational thoughts you are having may not be as wierd as you think. OCD can cause people to obsess over some pretty crazy things. Have you been diagnosed with OCD or is this just a hunch? I have mild OCD and at one stage in my life I couldn't drink out of glasses unless I had checked them over. I was sure there were drugs in the bottom. Rationally I knew there weren't but still I just HAD to check, every time. This messed up my social life let me tell you.
I got over this particular obsession by using CBT and by forcing myself to out to a cafe and order a drink, and then drink it...it was scary but it passed. You say these obsession/thoughts are going on for months. I'm really not an expert so I don't know what is "normal" but honestly you are most likely not alone in this. We have quite a few other members who have OCD and they may have some more tips for you. I find when I have these thoughts I have to go out and challenge them, or if I can't then I need to journal about them or talk to a therapist.
Please don't feel you are alone in feeling these things. If it is seriously worrying you please see a health professional okay?
Cheers, Meg