My youngest granddaughter is 6 weeks old. Eating all the time is typical. However, he might not be getting enough to fill him up at each feeding. My daughter said it takes 30-45 minutes for her little one to get full. But then she frequently doesn't eat again for 2-3 hours. But sometimes it's an hour later.
My daughter pumps and sometimes feeds her with a bottle because she drinks that faster. She also used this way to find out how much the baby needs to drink. She also supplements from time to time with formula and she does have less bowel movements when that happens. It's normal for that.
I suggest he may have gas which is causing him to be fussy and also to want to nurse more often. My daughter gives her baby "gas" drops. Mylicon is one brand, I think, but she gets the generic from Fred Meyer.
She also pumps her legs back and forth to her tummy and out.
Your baby may be having difficulty digesting the formula because he's lactose intolerant or allergic to milk protein. If he's fussy even when you nurse and has gas he may be reacting to the dairy that you're eating. Or to other foods that cause gas.
The way my granddaughter acts when she has gas is to fart often. And to be fussy. She fusses less when she's held. I suggest that at this age babies need to be held A LOT. It's a new world for them and they need the closeness.
You don't need to be concerned about constipation if he has a bm or two sometime during the day. Babies differ and some poop less often than others and usually poop less often when on formula.