Welcome! Your body is starved for nutrients after being vegan. You have to rebuild not only muscle but bone density, connective tissue, etc. Don't worry about the scale. Many of us come here from vegan, vegetarian or just conventional wisdom plans (only a playing card deck quantity of meat daily, only x eggs/week, no saturated fat, etc. ad nauseum.) I suggest The Vegetarian Myth by Kierre Keith to understand what veganism has done to your body. (Actually, I suggest it to everyone I meet.)
It was lying three days in a bed at Tulane Hospital that got me serious about my health.