sleep help

My child is 5 months old and has been on a consistent routine since about 3 months. He sleeps through the night and self soothes at night. He was a good day sleeper until the 4 month regression. On average he sleeps good in the morning. Anywhere from 1-2.5 hours butnits not consistent. He really struggles in the afternoon. He wakes anywhere from 30-45 minutes. I give him time to try and self soothe but he either cries or starts playing. I try patting him back to sleep but he is usually up anywhere for 30 min to an hour and sometimes he doesn't go back to sleep. I'm very consistent with him so I know it's not schedule. I tried shortening his wake time to see if he I'd over tired but that didn't make a difference today. Any help would be appreciated.