I don't remember when exactly it started, but The Jungle Book likely had a part. But the bigger draw for me was Last of the Mohicans, Dances With Wolves and Indian in the Cupboard. That last one was probably even my first actual crush, though I wouldn't admit it until only a couple years ago when I came out as gay. But yeah, ever since I can remember, I've found myself attracted to men in loincloths of all types, but breechclouts especially.
As for creating my own, I haven't really had the confidence to try it. But I have bought some pre-made ones. I have a wool breechclout I wear for reenacting that I think I posted a while back, but I wear it with a lot of other gear as well. I'm not confident enough in my physical shape to go shirtless! Maybe one day... I do look forward to being able to kit up again though.
I am very glad that you discovered your sexual orientation at the same time because of your liking for men in loincloths. Just like you, the same happened to me, only with me it was for the movie "The Jungle Book of 1994" and having my "first crush." I hope one day you will be encouraged to go out without a shirt and have confidence in yourself ;)
I cannot really say what started my interests in loincoths. It must be the time when my puberty started. I can remember that I saw some ducumentaries and read some books on foreign countries with picture showing men wearing various types of such gear. I was fascinated and still am, both with men and loincloths.
I soon started to make my own loincloths, first just two flaps, later I improved the design. I still wear my gear in summer when out for hiking or camping.