How do you know if you have OCD?

I have to do everything in numbers like 3,5,9,12,15 and 22. It enrages me and I keep trying to stop. I am a teenager and this has been happening for about 2 months. This has happened when I was about 8 and it went away after I don't know how long. It's back now and it seems much worse. Do I have OCD or is this just a thing.