According to Scott Alexander's review (https://slatestarcodex.com/2018/07/10/melatonin-much-more-th...), 0.3mg is the correct dosage for melatonin and higher doses might do more harm than good. I think you have accidentally replicated some of the melatonin research on yourself.

I personally wouldn't want to use melatonin all the time. Relying on a drug to keep my circadian rhythm going seems fragile and scary.