Low vitamin D3 levels can weaken the immune system and predispose you to an autoimmune disease. You would need to get a blood level
done. Having a level of 30 is good, but when you have an autoimmune disease, your level should be at 50 or higher, Vitamin D3 can be purchased in the grocery stores or vitamin stores and on the internet. It is very inexpensive. If your level is low, you should be on at least 2,000 units a day.
I don't know much about seratonin.