G'day

Im curious....I have this kind of 'gap' of, well, nothing, between the bottom of my rib cage, under my boobs and down to the bottom ribs iykwim. If I push on it, it feels all squishy and kinda hurts. Does anyone know if this could be seperated muscles or what else it could be? If it is seperated muscle how do I fix it (if it can be)? Im starting to worry cause DD isnt exactly a tiny baby anymore.

Thanks for any help x