Sorry if this is a stupid question but...

Baby is ebf now 12 weeks old. She prefers the right side over left and today I noticed that my right side was still really heavy and feels kind of hard after feeding her. Not really sore or any of symptoms. It has me worried sick. Can breast tissue change and become more dense while breastfeeding? Has this happened to anyone else before one the boob that baby nurses from more? Hoping for some words of kindness and comfort. Tia