This is what I can advise from my own experience:
I have a baby boy who is 7.5 months old. He got croup/laryngitis when he was about 5 months old. It lasted about 4-5 days before it got a bit better, about 8-9 days for full recovery. He was also put on nebulizing med (albuterol), which we did for about 3-4 days as needed and when he showed signs of difficult breathing. What made the difference for us was steaming him in hot showers.
I would take a scolding hot water (I naturally LOVE hot water so it was no problem for me) and my husband would hold him in the bathroom as the mirrors were fogging up. Or we would just run hot water for about 10-15 min (water heater will of course eventually empty out) and stay with him in the bathroom holding him up, rocking him, singing to him, etc. We stayed with him in the bathroom like this 5-6 times each night for about 4-5 days. Those were nights from hell and we slept maybe 1 hour total, if that but that paid off nicely.
Definitely change a doctor. we also have had issues with our pediatrician. Because this is our first-time baby, we would always rush in at the sign of a little trouble. There were times when we made doctors visits every other day (seriously!) for about 4 weeks straight. We came to the conclusion that we learn nothing new with each subsequent visit, we get more frustrated, we get no answers and the baby is still sick, not getting better, etc. I learned to trust my own instincts to do logical parenting and consult books and blogs and that has been more helpful than doctors. Doctors frankly have the tendency to complicate things more than is necessary (emergencies aside, of course). Make sure your baby is well hydrated and gets plenty of rest. Check the fever, make sure baby is breathing well and if it is neither of the above, then stay home and take it easy with the baby and spare yourself another frustration at the doctor's office. After the frustration we went through, we have never looked back. Our son is as healthy as can be and I do not want to see another doctor (except mandated well checks, immunizations and emergency situations, of course) as long as we shall live. WE HATE DOCTORS! Instead of helping our son, ours was telling is 'to ride it out because babies get 10-12 colds a year and that's what we have to deal with' (direct quote).
For that 'advice', we paid $1,200 (well, our insurance did) each time we saw his pediatrician for 15-20 minutes.
Do yourself a favor and stay home with your baby. That's a better use of your time than hanging around doctors' offices.
