My daughter is now 2 1/2 and is doing much better but starting at 5 months she had her first cold....which instantly turned into wheezing, we have struggled with controlling her asthma ever since. I will not bore or scare you with all the details, but if your doctor thinks he needs prednisone, please give it to him. My daughter has unfortunately taken it many times. She is now well controlled due to several asthma medications, and a cold remains just a cold. She has suffered no side effects from the many times she has had to take steroids. If you are truly worried, or questioning your pediatrician get a second opinion or ask to see a specialist. Hope he feels better soon!!
I agree with Madhouse re looking at ribs. Also, if LO does not like the mask then one tip is to squirt the inhaler into the mask before you put it to the face and then hold it there - it sounds awful but if they are crying then they are taking deep breaths which is actually a good thing iyswim.
My 4yr old was v similar and has got better over the years if that is any consolation. You also do get to recognise the signs! They don't tend to worry if they are still alert and eating but if your child is like mine then he would eat whatever the situation so I had to make a bit more of a fuss. General rule of thumb is if worried then call the out of hours people. Keep us posted