That's a common age for a "growth spurt". Baby will nurse until the flow slows, and then raise an almighty fuss about the reduced flow, and then subside when another letdown comes, and then repeat-- for hours, sometimes. That's cluster feeding, and it's nature's way of increasing your supply when it's no longer meeting baby's needs. You might notice baby yanking on your nipple, or popping on and off repeatedly, or beating your chest with fists, or kicking at you, too. Unfortunately for us mamas, it doesn't take babies very long to work out that this kind of fuss will very often elicit another letdown of milk. If you roll with it, and let it happen, usually it'll get better in a few days or a week, when the supply and demand even out again.
Sometimes if you take baby off the breast for ten or fifteen minutes, and try an alternate method of soothing, and then try nursing again, you can get another letdown of milk for baby. Also, you might try taking baby off for a burp-- sometimes the fuss is just the need to burp. Also, sometimes they fuss because they're overtired and can't get to sleep. Have you learned to nurse in a sling or carrier, or just holding baby and walking? That always helped my kids settle down, to nurse while I walked.
Lots of late-night nursing can help a lot, since your hormone levels peak during that time.
It can also help to switch sides every time baby pops off, even if it means you're using each side multiple times in a very short time. This is a supply-increasing technique called switch-nursing, and it can help make the supply catch up with the demand a little quicker.
