After 4 way heart bypass surgery. Many!

Hi, my dad has had a 4 way heart bypass last week and came out of hospital yesterday. As far as the surgery went, he's doing very well, however, since his operation, he has lost 5kg and can barely eat. He says that his lower stomach, back and front used to be in pain before the surgery but now it's intensified. It's a continuous pain that intensifies every now and again. They sent him for a scan and could see nothing. They also checked that he didn't catch a water infection from being catheterised and he hasn't. On top of all this, he has a terrible burning sensation on his tongue, his general mouth area and a sore throat. He says that everything burns, liquid and solid, and also tastes awful. Please could you shed some light on what is happening as it's causing major concern, many Thanks, Celeste