Help! American Flagfish

I have just lost 2 male lyretail mollies, and now my female American flagfish has a strange whiteish lump under its scales/skin. Also, it’s eyes seem to be bulging a bit.
You can see the whiteish lump thing just above and slightly to the right of the black spot on her side in pictures 1 and 3. Right now it is about the size of 2 or 3 of her scales.

Water stuff: Ammonia and nitrite: 0 ppm, nitrate: 10 ppm, pH: 7.5, temp: 77 degrees Fahrenheit, tank size: 20 gallon long

I know this isn’t the right thread for this, but yesterday when I posted this in the fish disease thread only one person answered, but they didn’t know what it was.

 

Were are the disease people?

 

I suspect this may be an internal parasite which creates a symptom of Popeye. Did the mollies also develop Popeye?
Is the Flagfish still eating?

 

The flagfish is acting normal, and I never noticed any popeye in the mollies. However, with the mollies, they would appear perfectly fine in the mornings before I left, but would be dead by the time I got home in the evenings. This happened 1 by 1 for 3 days in a row

 

Did you open any of them up to look for worms? I'd personally run a round of your favorite antihelminthic of choice on the tank and see if that makes any difference.

 

No, I didn’t open any up. And what do you recommend for helping it