What Causes Low Appetite In An Infant?

i HAVE A 6 MONTH OLD PREMIE BABY 35 WEEKER, HE HAS ALWAYS BEEN A STRUGGLE TO FEED, BUT LATELY IT IS GETTING WORST, THERE ARE DAYS THAT IT TAKES ME AN HOUR TO FEED HIM, HE IS CURRENTLY AT A HOME CARE PROVIDER AND HE IS WITH HER 11 HOURS A DAY, BUT HE ONLY EATS 11OZ TO 14 OZ IN THAT TIME. SO BY THE TIME I GET HIM I GET TO GIVE HIM 5 OZ. BY THE END OF THE DAY HE HAS ANYWHERE BETWEEN 15-28 OZ DEPENDING IFNI CAN GET ANOTEHR FEED AT HOME. I JUST RECENTLY STARTED GIVING HIM PUREE FOODS. TO HELP HIM GAINED WEIGHT. SOMETIMES WHEN HE DRINKS FROM THE BOTTLE THE MILK JUST COMES RIGHT OUT HIS MOUTH. I NEED HELP, IVE TRIED EVERYTHING TO GET HIM TO EAT. CAN THERE BE SOMETHING WITH HIS STOMACH THAT MAKES HIM NOT WANT TO EAT? FEEDING SHOULD COME NATURAL TO BABIES, BUT WITH MY BABY ITS A FIGHT.. PLEASE HELP!!!