16 month old may have pneumonia...very concerned!?

I took my 16 month old son to the doctor yesterday for a cough that was getting worse. The dr said he heard a little bit of crackling in his right lung, and it could be some minor pneumonia. He's now on an antibiotic, a steriod, and breathing treatment 3x per day. He has no fever, and is acting normal (eating, drinking and playing). I'm just terrified that it will get worse and he'll end up in the hospital! Last night I thought he was breathing more quickly than normal, but my husband thought it was fine. I also think he was breathing like that at the doctor, and he didn't seem to be concerned with it, but I just can't stop worrying!