Its very normal to need to go up a size after childbirth! I would get the next size up and see.
Size A is the bigger size with the moon cup . It’s designed for women over 30 and women who have given birth vaginally. Is there bigger ?
My mistake! I assumed A was smallest like the first in the alphabet 😅 in that case I'd maybe try either a smaller size mooncup (as if its too big it can also cause leaking as it might not open properly) or perhaps a different brand goes bigger?
You may have the wrong size. It's also possible that your cervix isn't fully contained in the cup. Stick a clean finger in after inserting and go around the outside to make sure it's fully open and your cervix is fully contained