With Reflux they sometimes don't treat at first, it often it takes you going back to the GP and pushing - is he gaining weight?
Are there other symptoms that could point to cows milk allergy or similar?
Also although quite rare something to be aware of is Pyloric Stenosis -
The below is cut & paste from http://www.gosh.nhs.uk/medical-information/pyloric-stenosis]
What are the symptoms of pyloric stenosis?
In most cases, a baby with pyloric stenosis will begin bringing up small amounts of milk after feeding. Over a few days this will become worse until the baby can no longer keep any milk down. This vomiting may become so forceful that the milk may be projected for several feet out of the baby’s mouth. This is called projectile vomiting.
As the milk is lying in the acid in the stomach, it can curdle and become yellow in colour. This also reduces the amount of faeces (poo) passed, as little or no food is reaching the bowel.
If the condition is not treated, the baby will become dehydrated and not gain weight. Signs of dehydration include lethargy, wet nappies less frequently than normal and the soft spot (fontanel) on the top of the head may be sunken.
What causes pyloric stenosis and how common is it?
Pyloric stenosis is a fairly common reason for babies needing an operation and usually develops around six weeks after birth. We do not know exactly why pyloric stenosis develops, but it tends to affect more boys than girls, and seems to run in families too.
How is pyloric stenosis diagnosed?
The thickened pyloric muscle can be felt, especially during feeding, as a small, hard lump on the right side of the baby’s stomach. The muscles around the stomach can sometimes be seen straining, moving from left to right as they try to push milk through the pylorus.
Your child’s doctor will ask you lots of questions and may want to examine your baby during a feed to observe any vomiting.
Sometimes the doctors may want to confirm the diagnosis using tests and scans. These can include an ultrasound scan, like the ones used in pregnancy, to get a picture of the thickened muscle.