Is my 3-month-old going through a growth spurt or is she just hungry?

My 3-month-old was sleeping through the night last week for a week. This week, she wakes up more than she ever has. Is she going through a growth spurt or is she hungry? She eats right before bedtime so I'm pretty sure she has a full tummy.

It sounds like she is going through a growth spurt so she may be hungry. That is very usual for three months. If you're breastfeeding, her increased feeding will increase your milk production to match her need. You had an unusual break last week. Young infants like yours rarely sleep through the night. Give her a few minutes after a cry to see if she can settle herself back to sleep. Don't let her get frantic. Feed her when she gives you a hunger cry. Rest during the day yourself so you can keep up your energy. Look at "Sleeping: 4 months" for more information on managing sleep issues at this age.