Actually, the myelin sheath is the protective/insulation sheath that surrounds the axons. Yes, B-12 helps with its repair. Signals do not transmit well if the insulation layer is poor. OCD is often related to weaknesses in how these signals transmit.

There is evidence that suggests that magnesium deficiency contributes to ADHD. Google magnesium and ADHD. Mag is known for its calming effect. Whether there is an interaction issue with ADHD meds, I could not find any.

I don't take 3 grams of fish oil. Many recommend that much. I take one large liquid filled softgel pill. There are versions with high concentrations of the Omega 3.

I am surprised you have not used facts to over-rule some of your OCD issues. The insecticide issue should be easy to resolve. The PartsPerMillion to achieve toxicity should be available. You'd have to wipe down the panels then eat the wipe to even start to ingest a measurable level. Same goes for the dish towel except I expect the dishtowel is used on dishes after they have been rinsed with clean water.

Use your analytical mind to resolve these issues. That is what CBT is about. BTW, People are living longer that ever before. If these chemicals were dangerous, why do we live so long? You have many other issues in your life that create a risk of many magnitudes higher.

Supplements could enhance the value of your psychological help.