Its is very difficult to make a diagnosis on external disease/parasites,never mind internal parasites.Most internal parasites show the same symptoms-either a pinched or swollen abdomen,off color,stringy feces(usually white),spitting out food,gagging motions and fish may stop eating.
I have bought numerous wild-caught fish and have seen this several times.A lot of these parasites are very difficult to get rid of.My old thinking was to treat w/mild medicines,trying not to stress the fish out furthur.If the parasites are not destroyed,the fish will probably also end up w/ a bacterial infection and recovery is slim.If the fish are still eating,treat w/Jungle anti-parasite food.if they don't eat that, mix metronidazole in w/your food and the fresh garlic.Following the directions,I would use the Praziquantel.Metronidazole can also be added to the tank water.Salt may also help.I do water changes daily or every other day when treating fish.Make sure to addv xtra meds. that were taken out w/ the water changes.
I have has success w/ Fluke Tabs.I used meds. in the food also while using Fluke Tabs.
I don't know your situation-Quarantine tank,if not, other fish in your tank etc.Whatever;if your fish has internal parasites/worms,I would not be afraid to overtreat rather then undertreat.
Read everything you can about them and good luck.
Tom