If melatonin works for you, great! I’ve tried 2.5mg, 5mg, and 10mg melatonin… zero effect. (Maybe a slight headache with 10mg sometimes, though that might just be my imagination.)
Someone else I know, can take 5mg melatonin and be out within minutes.
I suppose it all depends what the underlying cause of insomnia is, and how your body reacts to melatonin.
Other things to try: OTC sleep drugs containing diphenhydramine, or just take Gravol (or generic), it’s the same thing and a lot cheaper. It seems to make most people drowsy. Hit & miss, IMO, but it’s worth a try. I find that if it works, it works well; if it doesn’t work, it makes the night awful.
After that, you pretty-much have to get a prescription for something stronger. There will be some prescription drugs that will work (it probably will not be the first one you try), but they come with more serious issues of dependency.
Non-drug approaches are various behavior-modification therapies. Most is common-sense, but for people without common-sense it can help a lot, and it has no down-side.
Stay away from psuedo-scientific nonsense, or “ancient Chinese” medicine. All those new-age things will do is take your money.
Finally, be aware that not everyone needs 8 hours of sleep. Some people can be perfectly fine with 6 hours or even less. If you wake up after 5 hours of sleep and feel wide awake, just get up and enjoy the extra 3 hours of free time that day!