Not to stress you out any more than you already are, but you MUSt not give up just because this child is fighting you.
If you cant get this baby to eat or drink then you may end up having an N-G tube installed. It is not exactly what you want to hear, but I have to tell you, there is no better way to get calories into this kid and get him up in weight a few pounds. Nutrition is of utmost importance.
What happens is this: As nutrition declines, these kids tend to spiral down quicker. In other words, they gain momentum going the wrong way. Sometimes you NEED to kick start the system by getting his strength and nutrition up with a feeding tube. It may only have to be installed for a couple of months, but its effects are long lasting once that kid gains a few pounds. He may actually be a different kid--more energy and a better appetite.
Many studies have shown that low body weight is related to faster decline in lung function.
This baby should continue to make gains in weight just like any other kid. It may come on at a slower pace, but baby should grow.
Another suggestion is sometimes you may need to change enzymes. They are not all the same. We use pancrecarb which contains bicarb as a buffer. It makes the enzymes work better. Some people use zantac with enzymes to make them work better also. The gut is very acidic in CF and enzymes dont work well in an acidic environment. Also, the pancreas lacks the ability to secrete bicarb into the duodenum.
Get MCT oil which you can add to some foods to increase calories.
Also, make sure you get vitamins into him. Most docs recommend ADEK's I personally dont think they are the best, but these fat soluable vitamins are formulated to be bioavailable to CF patients.
Stay away from Calcium, and increase Magnesium. Also, get him liking cruciferous vegetables, like broccoli, coliflower, kale, sprouts, etc. www.sharktank.org
Dont let his poor eating go too long without getting him to his CF specialist. I suggest you dont use a pediatrician, you should find a CF specialist.
How is his weight now and percentage on the growth chart?
Have you made any gains in weight/length since diagnosis?
Is this baby by chance still breast feeding or bottle feeding?