4 month old suddenly fussy

Hello, first time parent here. My son turned 4 months a week ago, he was never a fussy baby, and all of a sudden henis getting very fussy during the day, whining out of nowhere, wont stay in the stroller long before he starts whining. I have a hard time getting him to sleep during the day, over the night he luckily sleeps very well. He doesnt seem to have any symptoms like diarrhea or fever or something, any advice on this?