If you are coughing up brown stuff you are dehydrated. I was just like you when I had my surgery in May. I could not eat nor drink and I was coffee up brown stuff. I had to be admitted in the hospital had a very bad case of dehydration and my kidney was not doing good either. However I made it through and all is good now.
Premier Nutrition is a very good shake each shake has 30grams of protein and 160 calories it come in Chocolate, Vanila and I just found Strawberry. You can get it from costco if comes with 18 shakes for $25.00 or you can look it up on line. Amazon recently had a really good sell on the shake 12 for $7.00 I bought 4 boxes for $28.00 and 48 bottles of shakes. It is one of the best I have tasted.