Thanks for your replies they are so helpful.

Chrispe he is 4.5 years old. He had two doses of the amoxicillin last night and was so much better. Not as much coughing. Can't hear the wheezing anymore. Lots of energy today.

Would asthma pop up when he's sick or is it more likely to be related to his eat infection and congestion?

DH has asthma but got it as an adult. DS has allergies to nuts. I'm wondering if he's allergic to something else. Could that cause the problem? I think I need to get him retested again.
Sounds like the amoxicillin is doing its job! It could possibly be what they call 'viral asthma' which means it might show when he has a flu, ear, or chest infection. Or it could be that a bit of mucus was just in the passages (which is different to asthma)
So glad to hear that's he is on the mend!