What you mean by shallow? Shouldn't I take deep breaths?
I can't even breath shallow as I have to give it my all to even finish the set
Ignore that keep your breathing normally.
I had a similar issue when I started out, use DBs, get a nice deep stretch at the bottom, at the top you want to be squeezing your pecs together. Do that to failure, it's easier with DBs because you can just drop them, and you get a better range of motion and deeper stretch. You have to really push it to failure though like it feels you're having a heart attack (you're not it's just the muscle). That is what I had to get over. I could go to failure or 1-2 reps shy on every exercise but chest was a bit scary just felt different, more internal. Chest needs to take a battering to grow (in my experience) compared to like shoulder where I throw some weight around and they blow up.
I'm 90% sure you have the same issue (not pushing yourself hard enough). Do it next push day and let me know. Also, do chest first and leave shoulders for after. OHP can be a struggle after you smash chest but just prioritise it for as bit, shoulders need less work anyway.
You can even drop a leg day for rest: PPLrestPPrestPPLrestPPrest - extra day recovery will help blow up your upper body. It's what I do now as my legs are very solid and felt burnout going 6 days a week.