HELP Baby won't nap during the day

My 10 week old refuses to nap during the day which leaves him cranky and overtired in the evening. He's been good at night getting approx. 11 hours but not napping during the day is taking a toll on him. 
If I am lucky enough to get him to nap when I notice he's overstimulated or getting tired he only sleeps for maybe 20 minutes. The only place he loves is the changing pad so I have to stand beside him if he falls asleep there. 
Any suggestions?