My DD is 6 and a half weeks and in the last 2 weeks she only gained 90 grams is this normal I'm exclusively BFing and the week before that she gained 170 and the week before 20 I'm so confused shouldn't she be gaining more weight she's feeding about 6 times a day and sleeping for 7-8 hours at night having wet and soiled nappies every change seems happy and the nurse doesn't seem worried so why am I?