My baby came 4 weeks early & had to use a nipple shield due to me having flat nipples. i use the tiny 20 mm one and now he’s 1 month and the base of my nipple is red and irritated due to either the nipple shield being too little now or i’m not sure. I’m thinking of going up a size but it jumps to 24 mm and he doesn’t latch on to that one as good but it feels better for me. What should i do? are you supposed to go up a size as they grow anyways or stick with the same size?