Hi!! My baby is about 3.5 months old. Lately, when feeding her, she plays with the bottle a lot and seems to take her sweet time. Feeding her these days takes a minimum of 30 minutes, and sometimes an hour! If she starts taking longer, I'm going to have to give her new formula during the feeding, since it's only good for an hour. She's still using the slow (level 1) nipples...do you think it's time for me to move her up a size?