How much weight shud my baby gain a week?

she is 8wks old,10lb2oz birth weight, fed. during the day she feeds almost every hour and quite unsettled... but at night she has feed bout 8.30-9pm and sleeps till 4-5am has quick top up and then sleeps again till 7.30ish. in last 3 weeks she has only put 3 oz on. Although she big at birth she is not chubby she was 55cm in length.