I would look into neurofeedback for OCD. People with this condition have dominant excessively high brainwave frequencies, which keep them in a state of hypervigilance. If you don't have biofeedback/neurofeedback clinics in your area, it might help to listen to relaxation recordings.
The Alpha-Stim is also supposed to help with OCD. You can use it at home. There's tons of info about the Alpha-Stim if you google it.
Zoloft nearly killed me-results there vary! I view OCD as: heat in the brain, everything is firing rapidly, yet we ME types are also fog-ridden. Wired/Tired often. I think 45 thoughts for each two other people think, and thats exhausting. I know very smart people who are affected by this. Highly Sensitive People (HSPs, also...) Thoughts are what our brains do. Change your relationship to the thoughts, slow it all down. Breathe. Chose to put less weight on random thoughts. It was just a thought. And make sure you've got your house keys! And frankly: well, about 1/4 of a 0.5 mg Xanax helps me with this alot, somehow! I'll stop thinking that same thought, about 15 minutes after I take part of a pill (which I don't do very often, pill averse).
GABA deficiency is shown to correlate with OCD. GABA and glutamate fight against each other, too much glutamate then OCD, anxiety, ADD, insomnia etc. Glutamate pushes GABA out of the neurons.
Magnesium and Vitamin B6 (both mentioned by other posters) are needed for GABA production. I also found great help by taking GABA (300mg or so) dissolved under the tongue and no effect from swallowing the capsule. This changed my life for the better, one of the best treatments!
I have found GABA, inositol, glycine, bone broths, minerals with extra lithium orotate, systemic enzymes, Vits. A and D or cod liver oil, ox bile acids, magnesium malate, all quite helpful. That is the calming side.
For thinking more clearly, I used iodine drops, L-carnitine, Acetyl-L-Carnitine, CoQ10. I have just started testing using branch chain amino acids.
I also eat a low-carb, adequate-protein, high-fat diet, which is very low in naturally occurring food chemicals, and as free of man-made chemicals as I can manage. Info on avoiding the chemicals: