500 ug of B-12 is a small dose and likely cyanocobalamin, not methylcobalamin. 1000 ug or even 2500 ug (mcgs is the more common unit in the US)

The lab standards are low. My doctor wants to see about 1000 pcgms/mL for B-12. Blood levels do not always indicate cellular absorption levels.

I was struggling with the same symptoms in a much more pronounced way and B-12 shots and mega-nutrition made a huge difference. Again, you symptoms sound more like depression than PCS.

Some research suggests probiotics can help, such as Bifidobacterium, Lactobacillus, and Lactococcus (these three types of bacteria that have been shown in the past to mitigate anxiety and depression).

Have you have sex hormones tested ? Testosterone, Progesterone, Estradiol, DHEA, etc.?

From Drugs.com:

"Some MEDICINES MAY INTERACT with quetiapine. Tell your health care provider if you are taking any other medicines, especially any of the following:

Many prescription and nonprescription medicines (eg, used for cancer, depression or other mental or mood problems, hepatitis C, high blood pressure, HIV, infections, inflammation, irregular heartbeat or other heart problems, narcotic abuse or dependence, nausea or vomiting, pain, Parkinson disease, restless legs syndrome, seizures, stomach or bowel problems, trouble sleeping), multivitamin products, or herbal or dietary supplements (eg, herbal teas, coenzyme Q10, garlic, ginseng, ginkgo, St. John's wort) because they may interact with quetiapine. Ask your doctor or pharmacist if you are unsure if any of your medicines might interact with quetiapine"

You are taking quite a few that are on the interactions list, including some that are included in a branded product.