chances are, shes having a huge growth spurt. (from what i have heard this is more common in breastfed babies because breastmilk is the most perfect food for infants! CONGRATS and THANK YOU for breastfeeding btw!)
so when they grow, because breastmilk is perfect food, its quite possible that she is using every calorie to use for growth and all of that. as long as she eventually goes, and it isnt hard or bloody, this is probably just fine.
fussiness comes and goes with infants. its possible she is more hungry than you realize more often than you realize. the most important part of breastfeeding is feeding on demand because breastmilk supply is determined by the amount of times and the length of time she is activley nursing; whether for comfort or for food. so nurse her first when shes fussy; comfort nursing is just as important as food nursing because it is what boosts your supply for an upcoming growth spurt.
also, major growth developments affect baby behavior. any time she makes a milestone, it interrupts her sleep, and might cause her to be a bit cranky because even if she can roll over one way, maybe she isnt doing it on purpose, and she doesnt want to be rolled over... you know?
or maybe shes cutting a tooth! my son had pains at 3-4 months (the doctor said gums looked white, irritated, and painful or osmething like that - there was a bump to them too) so even though he didnt actually cut them until 7 months, he was feeling it long before that. try some tylenol or pain reliever at especially fussy times to see if theres some kind of teething pain.
also try bath and or baby massage during times when shes fussy. OR, try giving her a toy or something and letting her be alone. maybe she either needs attention or shes over stimulated and just needs to chill out.
pumping her legs will help her pass any gas, you pedal her legs like on a bike, and then you can push them up against her stomach - i used to do this with both my son and 2 babies ive had in my child care the past couple years and it works like a charm. sometimes, turning them on their side and stretching a leg over and doing the other side also helps.
one thing thats for sure, infants are not known for their regularity. sleep is not ever going to be stable, neither is fussiness or the lack of it. infants are continually growing and changing and just when you get used to something, they do something different. just go with the flow, listen to her, listen to your heart, and do what you know is best. you are the mom you have the instincts for a reason, and the more you use them the more they grow. i can attest to that personally. :) it works for LIFE if you keep doing it now. amazing!!