I'm sorry to hear that it was not sustainable for you. It is not a rare occasion for many people who give a chance to transition to a vegan diet.

The vegan diet does not consist of merely eating cucumber and cabbage. You got to make some research and acquire some knowledge about diet and nutrition in general. It is also quite possible to adopt an unhealthy vegan diet. (Oreos and coca cola are vegan, right? ) Vegan diet also requires some behavioral modification. So it might be not easy for many now.

p.s: If I made any grammar mistake in this post please let me know.