Hi! Of course, I can't speak for a doc, but I'm thinking Seroquel usually knocks folks right out, so I am a bit surprised that it didn't help you. I know it knocked me right out.
I'm also thinking that OTC stuff, or even Ambien, is likely to be weaker.
I know you want to sleep, and not being able to sleep is a miserable feeling, but are you sure you want to take even more powerful meds? I believe they can really get habit-forming. I suspect that's why your doc is encouraging you to try a non-med approach.
I know I didn't answer your question. Sorry. I also know what meds you use is between you and your doctor. I hope you can find something that will help you sleep soon.