Strange hollow belly on female GBR

[graphitebeans]

Hello everyone. I need to know if I can treat whatever has happened to my beautiful female GBR.
I don't even know where to start searching, so if we can keep things constructive it would be greatly appreciated.
I will note that I haven't been keeping up with my water changes in the past couple weeks as I've started a new job - I know this is bad, and I need to dedicate more time to my aquarium regardless of my work commitments.
Thank you for your help!

 

[strollo22]

Could be internal parasites. Has the fish been eating?


Sent from my iPhone using MonsterAquariaNetwork app

 

[graphitebeans]

She's been eating fine. The only thing I can notice that's wrong is the hollow belly, which is making her swim with her pectorals more than her tail. She's swimming to the top and bottom fine, and isn't just sitting in one place... It's very strange.
I'm going to hit the tank with some melafix to see if there's an improvement...