My 5 month old as extreme diarrhea!?

hes on an Antibiotics for an ear infection and hes also teething. for the past 4 days hes had really bad diarrhea, and hes butt is so raw. the doctor gave me a type of cream that i can use twice a day to help with the diaper rash but hes still got diarrhea. they told me i could only give him pedialyte once a day and i dont know what to do anymore. hes not fussy or running a fever. he just has a messy diaper about every 10 minutes, an its so bad it comes out the sides! what should i do>