One of the issues with new vegans is that they just pull the meat or fish out of their diet without replacing it with the same calories and protein from a vegan source.
Until you get your diet in sync, you should get one of the vegan protein shakes, and drink one after your workout to kill the cravings.
These are in America, but I'm sure you have similar sources in England, and it has some info on the best ways to pick out a protein powder.
19 Muscle-Building Vegan Protein Powders That Actually Taste Good
I would suggest one of the vegan meal plans for athletes:
The Vegan Cookbook for Athletes: 101 Recipes and 3 Meal Plans to Build Endurance and Strength
The No Meat Athlete Cookbook: Whole Food, Plant-Based Recipes to Fuel Your Workouts―and the Rest of Your Life