I would definitely focus on post work out nutrition.
After workouts the body tends to go in starvation mode, combined with cortisol levels if you dont eat a postworkout meal or at least protein shake you will lose muscle mass guaranteed.
I would suggest either buying your protein in a product that comes in packets. OR pour your protein powder into a well sealed plastic baggie.
If you use water, and only use protein your body will use the protein but it will need carbs and a little fat (not too much fat after working out. Increase to normal fat intake in your meal about 2 hours later)
Ingesting fat after your workout tends to slow down digestion, while satisfying, you will increase the time it takes for the body to digest the protein, break it down into amino acids and get it into your bloodstream and into your muscles.
Your post workout shake should be primarily Protein. Preferably the fast digesting Whey Protein Isolate. They say the Hydrolized kind is best for post workout. Supplement that with some BCAAs. And if at all possible some sort of simple carb.
If you buy a Vanilla flavor powder you can use fruit juice, or water, or milk.
You may want to get some Gatorade powder and mix it in your Vanilla protein powder with plenty of cold water and drink it immediately after working out.
In order to help you fight off the cortisol, and catabolic post workout effects, where your immune system even drops, try to consume plenty of Protein and a good amount of simple Carbohydrates after your workout. And to help make all this easier try to find some kind of all inclusive Post workout powder and drink some BEFORE your workout.
This will definitely help.
Any Pre workout supplement you take must include Creatine and BCAAs at the very least. So take some before (Im not talking about supps like a NOXplode and such. Im talking about uncaffeinated type nutrition drinks)
Some good supplements for pre and postworkout are
Cytosport Fast Twitch
and my favorite pre during and post is Betancourt BullRush RECELERATOR.
If you use milk obviously dont leave it stored some place unrefrigerated.
Remember protein and carbs post workout.
Protein, carbs, and fats in your regular meal approx 2 hours later.
Good luck.