Vegetarian and, even more so, Vegan diets often lead to B- vitamin deficiency due to the absence of animal protein in the diet. Especially Vit B12 deficiency which is found naturally in animal protein.
My advice will be to make sure that you take a good quality Vit B supplement which has the Vitamins in methylated form. This will ensure better absorption from the digestive tract. Also make sure that you consume enough plant based protein. Hemp, Pea and Rice protein powders are all good options.