Reflux peaks at 4 months!
One of the babies in my NCT group frequently projectile vomited but was happy and gained weight and grew really well so it was a mop and bucket problem.
My daughter was sick 4-5 times each feed but was miserable and also had silent reflux. She gained weight ok but she cried all day so needed high dose reflux treatment and had multiple food allergies
My sister projectile vomited every single feed and at 10 weeks was less than 1lb over birth weight and was readmitted for re feeding with thickened feeds and very early weaning. It didn't resolve until she was 2 and she was under the 0.4th percentile until she was 1. She continued to be frequently sick until she went vegan at 40. We think she probably had a dairy allergy like my daughter.
When it comes to managing reflux weight gain and how happy the baby is can dictate treatment. My daughter was sick less than the other baby in our group but she was happy and my baby wasn't so my daughter needed treatment and she didn't. My sister was a mostly happy baby but wasn't retaining enough milk to put on any weight she was only 7lb 10 at 10 weeks so she needed treatment. It was the 80s so there wasn't much on offer.
Step 1 is determining if its problematic reflux. Are they following their line? Are they happy. If so behavioural adjustments keeping them upright after a feed, pacing feeding etc.
My daughter actually couldn't be moved to the upright position without being sick so what we needed to do was keep her the same position she was fed in.
It might be worth getting the tongue tie checked again, it might have reattached. My daughter can stick her tongue out fine and in fact can touch her nose with her tongue but she struggles to lift her tongue to the roof of her mouth! The tongue time assessments she had only looked at in our mobility. I am not sure if she has a tie but I'm not longer confident that the assessments we did have when she was a baby were adequate to determine if she has a tie or not.
Step 2 thicken liquids - gaviscon and carobel are probably the most common. They can cause constipation my daughter also needed a stool softener because of this. You might consider thickening liquids even if you decide it's not problematic reflux it's worth a discussion with the GP or HV for advice
Step 3. Omperazole on prescription which reduces the acidity of the vomit and can helped reduce the reflux too.
Then it's looking at things like cmpa. It is worth talking through the possibility of cmpa with your GP if you struggle with dairy too. There can be family links with allergies