Fantail struggling, can’t open his mouth

[FadelessCash16]

My fantail has been struggling for a while. Acting very lethargic and not swimming around much. He has some weird red lump under his head which I think has now caused him to be unable to open its mouth. Looked everywhere and couldn’t find anything on what this is and what to do. Any help figuring this out would be amazing!

 

[FishGuest5123]

Poor baby. @Colin_T any idea?

 

[FadelessCash16]

Opened its mouth and the thing under the mouth is filling it up on the inside