Help transitioning to crib

I need some advice transitioning my 10 week old to his crib for naps. He is on a 3hr schedule and currently naps in his swing. I tried a week ago to transition his first nap of the day to his crib. After 4 days of 3hrs straight screaming with no nap, I was finally able to get him to go down for naps in his crib. The new struggle is he only sleeps for 15 minutes and then he's up. When this happens his whole day is thrown off. For my own sanity I put him in his swing the past 2 days where he slept 1.5 - 2 hours. Should I try making a different nap of the day in his crib or should I stick with his first nap of the day? I just don't know how to keep him asleep longer. HELP!