The omperazole probably won't stop the vomiting but it should ease discomfort from the vomiting. It a proton pump inhibitors (PPI), which means it reduces the amount of acid the body produces so that the baby spits of the vomit is gentler on their oesophagus.
For us the reflux increased from 3 to 8 weeks. It stabilised there for a bit and then increased again from 3 to 4 months. At 4.5 months I took out dairy and soya from my diet and saw a massive improvement.
For us we have a mix of dietary induced reflux and developmental. If I have eaten foods that upset her the reflux returns but it is also there when we haven't had any obvious triggers. It gets better as she gets bigger and stronger then she has a growth spurt and it returns again.
There are three medical treatments for reflux in babies. Generally if there isn't any warning flags like weight loss or obvious discomfort or refusal to feed etc they don't give any medications.
If there are symptoms that mean reflux needs treatment there are three therapeutic options. 1. Thicken the feed, for formula fed babies there are special reflux formulas that are thicker or there is gaviscon or carobel which can either be added to a bottle of formula (but not already thickened milk) or expressed milk or they can be prepared in a syringe or tea spoon to give alongside a breast feed. The downsides of thicken the milk as it goes in is that it can be too thick when it comes out and constipation can result. If this happens you can get lactulose on prescription which is a very gentle stool softener - it essentially a sugar syrup which was used to be the home remedy for constipation in infants in years gone by but don't do this, if you think it might be help speak to your gp about a lactulose prescription!
Treatment 2 reduce the amount of acid to reduce discomfort. This is where anti acids and PPI medication comes in. The most commonly prescribed at the moment seems to be omperazole but there are others out there too. Omperazole is very weight dependent so you need to keep track of the weight of your baby and their dose. If you are seeing minor improvements but still struggling with symptoms check that your Dr is moving up the dosage and not just weight increasing it. The starting dose is 0.7mg/kg (if baby is 3kg dose would be 2mg) I think often they get moved up to the next dose which is 1.4mg/kg (3kg baby now needs 4mg), the maximum dose is 3mg/kg. Our gp moved us up to 1.4mg/kg but stayed there it was only when we saw a different gp and then a paediatrician that said our dose should have been increased further after limited improvements once we got on the 3mg/kg dose we saw a noticeable improvement.
The third treatment option is domperidone it can only be prescribed by a paediatrician and only once other medication routes have been explored. In adults it is used as an anti nausea medication but the thought is that it can help speed up the time food leaves the stomach. If the milk spends less time in the stomach there is a shorter window for refluxing. It is an off label use and the evidence of it being beneficial isn't conclusive yet but it is an option for reflux that doesn't respond to meds.
We have taken quite a few foods out of my diet and we are on high dose omperazole. We did find gaviscon helped for a while but did find that she struggled to poo so we had lactulose on prescription too. Once she got bigger around 8 months we stopped seeing improvements when giving the gaviscon so we then managed to get a prescription for the domperidone which makes a big difference. Her reflux comes and goes so we only give it with feds on days where we can hear her refluxing.