A cold? Croup? Pneumonia?

Hi everyone! I’m here asking for lots of help. My 5 month old has had an off and on small cough for about 2 weeks and we would just joke he was faking it because that’s how small and dry it was. Fast forward to this past weekend, it became very mucousy and wet. Where he sometimes gags when he coughs or like he’s gagging at what he coughed up. I was bringing him in this morning once he wakes up, and I just noticed it now is wet/mucousy and has a little bark to it. What could this be? What should I have them test for/do? I know doctors sometimes miss things so I want a good thought going into this appt. he also has a low grade fever of 100.5.

I’d like to add that I work in a preschool/daycare and all the toddlers are sick with very bad coughs. We just went through strep and croup in there. My son does not go to the daycare but I could easily bring it home.