Baby with Bronchiolitis

I took my son to the hospital on friday bc his coughs didn’t sound ‘normal’ and they said he had bronchiolitis and was tested positive for RSV. We were prescribed with a mask and inhaler , the mask looks like the one you wear for general anesthesia. it was prescribed to lessen the mucus in his chest. it doesn’t do much. any tips to help loosen mucus in chest??? i don’t have a humidifier and sitting in my bathroom with the hot water running helps just a little bit and it doesn’t last too long