You are going to have to learn to prepare your own - or get Mum on side (I'm suer she'll be please if you tell hr you are trying to get healthy) - and take food with you.
Cold roast mart - chicken, beef, lamb. If you have to get take away (take out to you) BBQ chicken is your friend. If it has a coating you'll have to remove the skin as marinades and coatings have sugars in them.
Tell the swim coach your doctor has given you a list of foods and none of the things (crap) he is offering are on it and take your own.
I us to show horses, for over 40 years - again, take your own.
You have to take responsibility for your own health and make an effort.