Pulling/fussing at breast?!

Just the last few days, and not at every feeding, my 3 month old has been pulling away and arching his back pretty soon into our nursing sessions. He cries and doesn’t want to get back on. I try again maybe 10-20 mins later and he falls asleep eating but seems happy and not even hungry. I always feed him right after a nap.

I’m assuming it’s gas or reflux but how long do I let this continue before calling the doc? He’s still having plenty of wet diapers and poo so he’s eating enough but it’s wearing on me that he screaming in my face 2-3 times a day and that he’s uncomfortable. Always during the day at some point.