I have to touch things an even amount of times?

Hi, So this is really scaring me. This has been happening since I was maybe six years old and now I am fifteen. I have NEVER ever told anybody this, but when i touch something I have to touch it an even amount of times and then with the other hand also. If i brush by something i have to brush by it an even amount of times with the other side to. If i don't I feel like something REALLY bad is going to happen. Sometimes I have to do it about one hundred times. What is this... when i try not to do it i end up basically getting all anxious and have to go back to that same spot and do it again. Please help me. I dont know what to do. This has been happening for nine years!!!!!! Please help..! Emily