If you can/afford, you could try testing in Germany. There are better labs for that. Sorry cant remember ...thats one of the issue for me. Dont know if you need GP but I supose you need one.
Could be protozoa or bacterial also but anyway...
Maybe you could try dr.Amin new lab in Uk or a lab in Liverpool or Manchester cant remember the name Para something. It was linked to a university. Guess Soly has a point with a GP refferal. But try contacting them
If infection is already settled and gut brush border is affected you could lose weight. Thats one way. They also can affect glands also and substances absoption.
Did you noticed if any food increase urgency for peeing?