Baby sick advice!

So my little 10 week old ((5 week premature) has always been quite a sicky baby.. and has forcefully vomited occasionally since birth. He has done more so the last few weeks but every doctors/hospital trip they say he is fine, (which I know), is growing... but I can’t help but think there is underlying problem? I’m convinced he has pyloric stenosis, or would they have picked up on that by now? Is the forceful sick normal for some? Or am I going to have to wait until he gets really ill before he is diagnosed...?