I've got the same problem, and I only wear Bohyme hair... and I've tried all kinds of shine sprays, but they always leave my hair with an oily, sticky feeling.
I know this sounds like a funny question, but what kind of water do you have? Is it hard water, well water, soft water??? My boyfriend lives on a farm, and I absolutely CANNOT wash my extensions in his well water... not only do they end up dull, but the hair feels like it has a rough coating on it.
I did some research on the internet, and I read that some types of water will supposedly leave mineral deposits & residue on your skin & hair... to me, this theory makes sense, especially after my own experiences washing blond hair in well water and ending up with rust-colored highlights.
Anyways, I heard about a demineralizing product made by Malibu Wellness, and I tried it last week. I think it is absolutely AMAZING, I could not believe how bright & shiny my hair looked, and it's not that expensive.
Take a look at their website www.malibuwellness.com -- I bought the hard water demineralizer, Malibu crystal gel, and the sulfate-free shampoo & conditioner -- all three products are great!
Let me know if you want more information, I'd be more than happy to share my experience! When I was a teenager, I used to have wavy hair... as I got older, my hair started to straighten with a weird flip at the ends... after I used Malibu Wellness, my hair went wavy again, and I haven't had that in almost 20 years!!!