I did some research on what supplements may help the most with OCD, and aside from the ones like Ashwaghanda, I've found that vitamin B12 and folic acid actually showed signs of improvement for patients with OCD!
So even if you're not vegan, make sure you're getting your much needed intake of B12, as even 40% of people with an omnivore diet have B12 deficiency. I hope this information helps!