Does obssesive compulsive disorder symptoms include also being obsessed with the same thing or idea for a long period of time ?

Yes: Yes, you are right. Obsessive ideas are an important finding and often give rise to compulsatory behaviors with ocd. However, this is only one cause of obsessive ideas. Certain medication (including some for adhd) and other causes can also occasionally produce similar obsessive symptoms. Ask your doctor if you have any specific concerns. I hope this helps.