Hi, I stopped eating meat about three weeks ago. What supplements should I consider taking? B-12?

A supplement between 500 and 1200 mg per day should meet your needs. I tend to recommend the higher level since the body takes what it needs and eliminates the rest through the urine, so other than more yellow urine there is no risk of side effects with 1200 mg per day. In a few months, it would be interesting to have blood tests to make sure that your levels are optimal