I assume this is with tablets? In which case I think maybe try liquid solution instead? Sounds like either the tablets aren’t being absorbed at all or they are wildly off in the concentration (which is common because it’s so unregulated)

Just 1mg in liquid form is plenty for me, and that’s as someone who has had severe sleep onset difficulty for as long as I remember before I started using melatonin. I was told to hold the liquid under my tongue to absorb for a while before swallowing. I get it in 10mg/mL and it comes with a little oral syringe that you draw up 0.1mL with.