Bra Size

Struggling with my bra size since I am gaining more fats and breast is also becoming bigger due to pregnancy. Any tips momshies on how you choose your bra size? I tried google calculator but di ako kuntento sa sagot. I am currently wearing 36A bras from Avon. I'm confused whether i should wear 36B or 38A or 38B. Medyo nahihirapan na ako huminga kasi lalong sumisikip ang dibdib aside na congested na ang lungs.