I've been on and off melatonin for the past 5 years. Lower doses didn't really do anything for me. I'm nearly 30 and live in a high EMF environment. I found 10mg was good for a while, but started going up to 10-20-30-40mg. Closer to 40mg was too much, I'd have a really deep sleep and wake up alert after 5 hours, which I thought was perfect until I started nodding off around noon. The high doses also started a period of vivid dreams that seem to have calmed down now. In fact I sometimes have vivid dreams without the melatonin now, but didn't have many in the past.
I've reduced it back to 20-30mg depending on how tired I feel when it gets towards bedtime. Sometimes if I'm feeling sleepy enough I don't take it at all.
Edit: the brand was Puritan's Pride 10mg
That's a lot for someone your age ersio. Do you take it in an oral form? Or do you take sublingually? I noticed I needed well over 5 grams in the pill form but only 2.5 mg in a sublingual lozenge. If I take more, I wake up throughout the night, my sleep is shallow and I feel restless.
Given that you take such high amounts it must be very expensive. Maybe it would be worth trying out the sublingual version to see if you need less of it this way? It could save you some money. iHerb sells it quite cheap.