Problems with H&M nursing bras!

Not sure if this is the right group, but I didn't want to spend a lot of money on nursing bras so I got mine at H&M. I obviously ordered the same size in all of them, but the ones that are soft and unpadded are super small, like my boobs fall out small, and the ones that are more like regular bras are way too big, like one or two sizes too big. I'm so confused! Shouldn't the same size from the same company fit?! I've already used them so I can't return them either. This wanting to be cheap turned out to be really expensive. Anyone else had this issue with their nursing bras?