I do not like vegan diets for me personally but we can get enough protein from non-animal proteins if we are eating the right foods in the correct combination. Plant based diets allow you to actually eat more often and larger portion sizes. Animal proteins and fats make you feel full quicker and longer. When you exclude animal proteins you will get hungry sooner and are able to eat more often. Being able to eat more often is a pretty cool thing concerning protein synthesis. Research has shown that when we consume 30gr of protein we trigger protein synthesis that can last up to 3 hours.
The major problem concerning plant based diets for bodybuilders is that animal proteins are a complete source of amino acids while plants are not. On top of that the fiber in some plant based proteins can actually prevent the digestion and absorption of some amino acids. The feeling of of tiredness or lack of energy that Blast describes is not uncommon. This could be associated with your body not getting enough protein to provide for its energy needs.
There is no disputing some of the health benefits of a plant based diet but at the same time arguments can be made disputing those benefits. In my personal life I try to focus on a complete balanced diet when not in ketosis and as I get older I see the the importance of moderation.
SEMPER FI