soft spot on head

Okay so about a month or so ago I noticed my babies soft spot on her head really sunken in. I rushed her to the er and was told it was nothing st all. She was about one month old. From then on every now and then her soft spot gets sunken in a little but goes away soon. I've heard it's from dehydration. Well the past week or two it's been sunken in a lot more often. She's been sleeping a lot the past few days and not eating but every 3-4 hours. I breastfeed so I don't know exactly how much she eats. But she has plenty of wet and dirty diapers every day. Has anyone else experienced this soft spot thing? She has her two month checkup tomorrow so I'll be sure to ask her pediatrician. Just wanted to get opinions on here