I completly understand, because for awhile, I had the same problem.
I'd obsess over my guy and call him in the wee hours of the morning just to see what he was up to...
He got fed up with all of the stalking and broke up with me.
My advice to you would be to talk to your girlfriend about how your feeling.
Maybe you're feeling clingy because you're afraid of losing her? That's how I felt. I don't know, because I'm not you.
Soulsearching does wonders, and once you find the root of the problem, try talking to her about it, even if it seems awkward at the time.
You'll be better off when you do.