Is it normal to bloat after you haven't eaten for like 5 days and start eating again?

Yes, it is rather normal to get a little bloated when you start eating again after a prolonged fast. One thing to keep in mind--if you had the stomach flu, or you just weren't eating you have some atrophy or damage of your gut lining. So you won't be able to digest some things as well for a little while and you may need to work them back into your diet slowly. For example, you may be temporarily lactase deficient which will make you gassy if you drink milk or eat ice cream. I suggest starting with liquids and then advancing to simple carbs and eventually adding in more proteins, fats, and dairy until you are back on a regular diet over the course of a a few days.

yes it is normal because if you haven;t eaten, your stomach is obviously empty and is pretty much flat, once your start eating extends quite rapidly.

the bacteria in your stomach has suddenly been put back to work. the bacteria and acids in your stomach great gas and cause you to bloat.

Yes. It's probably water weight. If you don't eat for 5 days you probably got dehydrated and lost water weight. As soon as you eat you will bloat, plus your metabolism may have slowed down from not eating. If you start eating normally again this should go away, it isn't permanent