Get a blood test. You could have a micronutrient deficiency. It is common to develop either vitamin D, B or iron deficiencies when you cut meat since they just aren't as abundant outside of red meat and organ meat.

Would you care to elaborate on what you feel like when you try living on plants? What do you tend to eat? How long does it take before you start feeling like shit?

Judging by your last comment about it "not hitting the same" my initial thought is that the issue might not even be nutritional, possibly more psychological/subjective.

Don’t know what you’re missing because we don’t know everything you eat

Spinach gives iron so based off the information it’s not that

I end up feeling like absolute garbage.

Maybe, not cooking it well enough? Try changing your recipes, perhaps? Maybe more variety in spices?
Gram, pulses and dried beans (rehydrated before eating) with rice, tend to make my favourite recipes
and even though I use milk products, I feel pretty good even if it is lemonade with black-salt instead.

Maybe a shot of insulin, from the sounds of it.

Every plant is trying to kill you. It doesn't want to be eaten. It especially doesn't want you to eat its seeds. We can detoxify most of the ones that people eat, but it costs

Eating the same plants over again can make you sick

You may not be as good at detoxifying those plants as the people who do well eating them

I know I'm a lot healthier with no plants in my diet than I have been with lots of plants