You're worried about negative feedback suppressing hormone production/secretion.
Don't worry about your body decreasing melatonin production - it will do that regardless. The pineal gland in the brain is responsible for Melatonin secretion. This gland begins calcifying during puberty, and that calcification process continues throughout life.
The more the gland calcifies, the less Melatonin it secretes. That's why babies sleep...well...like a baby, and old people don't sleep for shit!
For what it's worth, I endorse Melatonin use 100%. But, you need to give it a fair chance. Some folks will notice immediate improvement, but many will need to take it consistently for up to a week to notice results.
It doesn't work for everyone, so don't bitch to me if it doesn't help you.