Have you been to a tropical disease clinic play?
They should do not only extensive stool but also serum and saliva tests there, if there is anything alien in you it should pop up.
Besides it might be more comforting to speak to a professional who sees real roundworms Tapeworms and flukes every day, and might be able to comfort you, with what you may have, or absolutely dont have.
It's a lonely world to spray your shotgun with a blindfold on.
Forget GP's and their standard Giardiasis tests, go straight to the travel clinic.