I’m not sure, but I know that when a family member had to do a low FODMAP diet, they couldn’t eat things with onions in them. But onion infused oil was fine because the sugars in the onion were water soluble, but not fat soluble so the oil didn’t contain the component they were avoiding. https://www.monashfodmap.com/blog/all-about-onion-garlic-and-infused-oils-on-the-low-fodmap-diet/
Not sure it’s related but it’s the first thing I thought of.
Hopefully this isn’t unwanted advice, but I have also cut out a lot of meat from my diet and I started getting weird side effects. (Lost feeling in my hands and feet, got dizzy a lot, felt extra stupid.)
After seeing a doctor, I take vitamin B and D supplements and it helped a lot. If you can’t see a doctor, you might consider trying some vitamin B and seeing if that helps. Apparently lots of vegetarians and vegans take it too.