I've had a good experience with Luvox (fluvoxamine) in particular the extended release version. I believe Luvox has been studied with respect to OCD.

One possibility is mindfulness meditation. It can be tricky for someone with OCD, for instance I have not had a good experience meditating unless I keep it to very small amounts done only in groups. But other people with OCD describe it as very helpful. Almost everyone who does mindfulness meditation, whether they have OCD or not, describes something similar to what you describe--incessant worry that never ends. It's just that in "normal" people it doesn't cause as much suffering or interfere with their lives as much.

You have already taken a step forward by noticing that the worry seems to have a life of its own, attaching to whatever is coming up as soon as the previous worry stops.