I just found this subreddit, and it was suggested that I try a 38M US (up from a 38H) after using the measurement tool. I will admit, it does fit very well, with one exception; unless I stay with my back straight all the time (which, I know, technically I should), the underwire digs into my ribs and hurts a lot. I've spent my entire life being told that bras in general are supposed to hurt, and that having red marks on my shoulders/breasts/abdomen after taking off my bra is normal, so I really don't know what IS normal. So is underwire just supposed to dig into you? Is my band size too small? Is there a way to remedy this?

EDIT: Since it's been asked a few times, here is my calculator measurements: https://i.imgur.com/inZQYf6.png