Flange size

When I first started breastfeeding and pumping the flange fit perfectly not my son is 7 weeks old and my nipples are starting to rub up against the sides, its not painful and my nipples arent sore afterwards. I went up a size and found that I'm getting hardly any milk when I pump with the bigger size compared to the "wrong" that's too small now. Has anyone else found that their flange fit at the beginning of nursing but now doesnt?