There's no scientific evidence supporting the idea that cravings are related to nutritional needs. Some of the most common cravings are for foods that have virtually no nutritional value (cookies, candy, cake...). Some people even crave dirt or other non-food substances. It's safe to say that your cravings for unvegan food don't have anything to do with a lack of nutrients.
However, feeling weak, tired and jittery could most definitely be related to deficiencies in iron, zinc or vitamins, and it could also be related to other factors like exercise or stress. If you can, see a doctor to evaluate your health status. I'm sure your friends and acquaintances mean well, but they don't have the knowledge and experience to judge your health status, and to suggest that eating meat and dairy will fix the problem is too simplistic, especially considering you had these problems before you became vegetarian.
