That is absolutely 100% a internal parasite. Those worms coming out are key symptoms good catch! I read that this will help with the worms levimisole I have heard mixed reviews about the severity of the disease and probably due to different treatments... one person said it wiped out their entire tank of 100 fish despite treatment and the other said their angels had it and treated it with levimisole. I would do your research but you need to start medicating ASAP or the fish will die. As parasites go they all steal nutrients so the fish will starve, that big belly isnt from food but from parasites growing in there