Nights are great, naps are a pain...

Hi! I am a FTM and my son is 17 weeks. He has been sleeping through the night for a few nights after we decided to move him to his crib in his room. He falls asleep nursing and I put him in his crib and he sleeps very good. When he wakes up in the middle of the night he soothes himself back to sleep unless he is hungry (which almost doesn't happen anymore since he started sleeping in his room). My problem is that at nap time he won't sleep in his crib. Even when I nurse him to help him fall asleep, he wakes up when I put him in his crib and won't soothe himself the way he does at night... I am thinking maybe it's not dark enough in his room? I tried to let him cry just a couple minutes, then go calm him, put him in bed again, wait a couple minutes if he cries, go back to call him...etc..... but that's not working. I know he is able to fall asleep by himself because he has done it before... and i know that he is tired because he is rubbing his eyes and yawning and looks ready to sleep. And i don't think he is over tired because I usually try to put him in his crib for naps at his first cue of tiredness.
So I end up keeping him in my arms or putting him in my bed and staying with him for his nap so I am sure he gets some sleep because if he doesn't nap he gets verrrrry cranky.
Any mom out there have this problem with their baby sleeping great at night but fighting nap times? Do you have any tips?
Thank you in advance!