Hello and welcome to the forum. Sorry you had covid. It can have such a different effect on people. Some people lose weight because while they think they are eating, it's less. And having diarrhea will impact your weight. Normally it does take a little while for this to happen but yes, you lose a high volume of water with loose, watery stool of diarrhea so that can become water weight loss in the short term. Let us know how you are doing now please.