My guinea pig pup turned 5 weeks old today,but she only weighs 120g.Is this bad??She only weighed 35-45g at birth,the whole litter weighed in that range because their mom is so small.She isn’t the runt of the litter,the runt has passed away recently.She has only been gaining a few grams everyday.She has unlimited alfalfa hay and pellets.She eats well,popcorns around the cage and is very talkative.Her tummy is round.