Don't worry ! If you already have a specific nutrition plan you need to follow because of your lactose and gluten intolerance, then start by buying the things you need to create those meals. Presumably, you had a plan in place before you had your surgery. Go back to those nutrition menus and plans.
You don't have to do anything extravagant. Start with some simple things first. Don't be afraid to go to the grocery store. Remember, while there may be some tempting things there, there are also lots of HEALTHY things there too. If you want to make a change to your life, you're going to have to do some things that take you out of your comfort zone. And right now, going to the grocery store is one of those things.
Well, you need to be brave. Don't worry ! Everything really will be fine. Just start with the simple stuff first. Don't think of shopping as something scary. Look at it as an adventure ! Think of all the wonderful things you will find !!