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Yes, she is probably going through a growth spurt...at these times they get hungrier more often, and need more intake. It's normal. Feed her.
A baby's sleep patterns and intake requirements change all the time... per their development and constant physical/cognitive changes.
Yes, it's tiring...but for the baby, it's not easy either. They wake for a reason.
If you do add formula....just do it for night time... you don't want to make it a habit all day, or it will probably affect your breastmilk production.
you can add the formula in a 50/50 ratio or a even just one ounce of it. But, this may or may not work. For some it does.
Many Moms, for various reasons, will mix formula with breastmilk for night-time and so Daddy can do this "job" letting Mom rest. It's okay... don't feel guilt about it... sure, they say breast is best...but I know for some situations some Moms need alternatives. Also, some babies may get used to the Formula... and then just prefer that. So keep that in mind. Others will reject Formula, so keep that in mind too. Each baby is different.
Also though, I would make sure she IS getting enough intake...and your production is fine. Sometimes, if they are not getting enough intake, they will wake more and be hungry all the time. As they grow, they naturally increase in their intake needs and requirements. But I think your baby is having a growth spurt.
Filling up a baby does not always "make" the baby sleep longer or better. Also, some babies during growth spurts need to cluster feed... and this is why they wake so much.
you need to go according to your baby's needs. It will pass... but I know it's tiring. Many more phases and sleep changes will occur, not to mention their teething wakings when that occurs... main thing is to keep consistent in your manner of aiding her. Babies and children thrive with a routine and consistency.
All the best,
Susan