I don't think there is anything stronger than Nytol over the counter here.
If you know anyone going to the USA soon, ask them to get you Unisom. It's very good.
Sorry, not an immediate solution, I know. Ask the doc for something else.
Tablets aren't that helpful, try and exercise in fresh air during the day, no caffeine in any form after about 2pm and no electronic screen use including TV for at least 2 hours before bedtime. Use an alarm clock if needed to make sure you get up on time. You won't fall asleep at 11pm if you have n't got up before 11am [ unless you are a teenager ! ]
look for relaxation CD's. This worked for me. My library used to have them so you could borrow them, like books. After a few nights of listening to these (I got two different ones from the library), I was sleeping like a baby. You can also buy them quite reasonably on eBay. Good luck
..wisgang'ssuggestion has a lot going for it. I often have trouble sleeping and Nitol sometimes works, sometimes not. But I have several therapeutic CDs forsleep, confidence etc. I have never reached the end of any of them without falling asleep. Use in bed at a quiet time.