destroying bad sleeping habits

my 5 month old will only nap or go to sleep if he's being fed or rocked. its completely impossible to keep up any longer and so infuriating when I see other babies just falling asleep by themselves. he sucks his thumb and can soothe himself to an extent. I'm just looking for advice on how to break the routine to get him to sleep. today I've refused to rock him and he's been awake for 8 hours straight and counting.. he doesn't get drowsy so I can't put him down half asleep. does anyone have any experience of this and advice?