What is the starting dose for Melatonin? Is this good for Insomnia?

Hi, a resident here told me about trying Melatonin. I have had a very difficult time sleeping. Only averaging about three hours a night. I go to sleep fairly easily, as I am prescribed 2mg in morning and 2mg at bedtime by Psychiatrist. However, I wake up always at 1 or 2am..and can't go back to sleep. I have spoken to her about this, and she just prescribes "sleep aids" that are basically sedating antihistamines..like Hydroxyzine, Clonodine, but it does very little for relaxation or staying asleep. She stopped them. Then she put me on Ambien but told me to take "as needed" only. However, I "needed" it every night. It stopped working after two months. She got upset because I took it every night. I pleaded with her for Sonata, as that used to help me, but she refuses..instead putting me on a very sedating antipsychotic called Seroquel. She said she prescribes a "low dose" for people with insomnia, when I expressed my concern about being put on that when I only have Major Depressive disorder, and panic attacks, that I am already on meds for. She prescribed 50mg. It does not help. I told her, and she increased to 100mg to no avail. A resident suggested Melatonin..but I don't know what dosage to start off with. Them I saw on a website, that people with Insomnia should not take this, only people with jet lag..I'm confused. Does anyone take this for Insomnia and how much? I have tried everything to no avail. I can't take herbs due to drug interactions. I don't do anything stimulating or drink caffeine before bed. Thanks for reading.