Hmmm, that is alot of questions at once really!
There are suggested preventatives for worms/parasites you can use, Food Grade Dietamacious Earth (spelled wrong?) added to the food and bedding for mites, worms, etc...Pumpkins seeds chopped and served alone or with yogurt can aid in treatment/prevention of worms, I have heard...I use both in my flock as well.
Gape worms Im not so sure of, never have dealt with...you can search right here on BYC and get overdosed with supportive information about it though, just go to search up above, and put in the keyword spot "gapeworm" and get a good cup of coffee or tea if you like! You should find something!
Oh....I had a young cockeral make a terrible noise for a week once, he had "sprained" his crower, and I know he did, cause I watched him do it!! He tried to outcrow the big boys when he first started crowing, and he literally hurt himself! He did just what you are describing your bird is doing? But he got all better, it wasnt a health issue, sorry.
Good Luck!
Tina