Sunken fontanelle at 7 mos.

Hi.my 7 month old has sunken fontanelle throughout the day. Even after few minutes of feeding it will be there. I checked with her pedia last month and she wasn't concerned as she is gaining weight and active and all. She said it's not only dehydration but could be other things like when she is crying or upset but i can still notice this is sunken even if she's just playful and all. Anyone got the same experience with their lo. She was 6.8 kg on her 6 month check up. Usually she has like 5 wet diapers during the day.