5 week old struggling to breathe with congestion

My almost 6 week old has had a virus for several days. I've been to the doctor 3 times and each time we've been he's been asleep and breathing fine. However at home after ever feed he is struggling fot breath due to mucus in his throat. We've just spent 30 minutes with him panting and coughing and gasping for air.

I see online it says that more than 60 breaths per second needs to be seen by a doctor and I've just timed his last episode and it's more than 60.

Do I take him back to the doctor again after they told me 3 times he just has a virus and to keep an eye on him? I've the doctor each time that he's finding it hard to breathe after feeding and they just keep saying "stay vigilant"

What on earth is the right thing to do?