Kierasmom,
Our son was on Pregestimil until recently - (and perhaps will go back if his new formula doesn't pan out) [Now we're on Enfamil ProSobee - yay!]. We had an NG tube and feeding pump until Thomas' 3rd month. You probably don't want to set the feed to more than 40-45cc/hr as we had problems with the "topping off" issue above that. We ran it at night and divided Thomas' remaining food budget by the number of hours during the night to ensure he made goal (I think goal was 750cc at the time). We were mixing it to 24 cal and then bumping it to 26 cal by adding a powdered glocose called Polycose. Ask your dietitian about this recipe:
1 cup packed (ish) Pregestimil
23 oz water
2Tbsp + 1tsp Polycose
This took our little on from the 10th - ish percentile to now the 50th in weight in 4 months. Have you doc or dietitian look into Neocate if Pregestimil isn't working. It's pricey - but I think further pre-broken down than Pregestimil.
I'm with you on the ostomy bag - a real bear. Our son was reconnected in August - thank God! Are you still battling the bag? Some days were better than others with the tube - but overall it worked. Fitting it into routine is important. Typically Thomas would've had his last round of treatments, eaten and gone to bed for a little while before we hooked him up and started the tube feed.
Good luck.