What you are already taking seems fine, although if you struggle to hold your weight I would make sure your post workout shake contains carbs as well as protein. Also i have found drinking glutamine during workouts to be helpful in maintaining that hard earned muscle! Be sure to eat every 2-3hours-plenty of meat and veg and good carbs.
Mix glutamine with water and sip during workouts then consume a shake with roughly 20-30g of whey protein and 50g carbs. You should be eating 6 ‘meals’ each day (breakfast, mid-morning snack, lunch, mid -afternoon snack, post training shake, evening meal and pre-bed snack)