If motrin is not working for him, and his fever is still going up, take him to the er right away!!
I have 4 children; 18 yo-girl, 16 yo-girl, 8 yo-boy, and almost 3 yo girl.
I have had my kids to the er many times, but fortunately, not for uncontrollable high fevers - but once. When my oldest started head start (1995), she brought home something that hit her pretty hard - her first real illness. She couldn't breathe without being propped up with pillows, couldn't lay flat, had a fever of 102 and vomited up her tylenol. I took her to er at 1:30 am. They had her sit up to sleep, gave her motrin for fever -she kept it down, and gave her oxygen mask to help her breathe. They said I could take her home -after an hour, but her fever wasn't responding to motrin, so I wouldn't leave! It took a 2nd dose -which they gave 2 hours after the 1st, before her temp started to come down. When she was breathing better and was able to lay flat without problem, I took her home!
If you are not happy with the results of the doctors, ask another one. Same with hospitals - if they are not helping, dont leave until you see changes!