3,5 month old nap refusal

Baby is 3.5 months. We are in the heart of leap 4. He sleeps 11 hours a night with one night feeding around 3:30 usually. Naps used to be about 45 minutes long every hour and a half (about 4 or 5 a day). But the last 2 days he has refused to nap. Yesterday he was especially fussy. Today he is as happy as can be but not sleeping. I finally got him to fall asleep after 4.5 hours and only because I put him in the baby wrap. Good lord. Is this the sleep regression? Or leap 4? Or an off couple days?