Susannah, you can try the melatonin again. I have found sometimes it takes a body a few days or weeks to get attuned to it. Diphenhydramine (Benadryl) helps most people but some folks react to it with hyperactivity. Chamomile and valerian work for many as well, but you have already tried those. Two more things you could try are "Happy Lights"--phototherapy lights in the morning, and heat. The phototherapy lights reset your own naturally-produced melatonin; 30-60 minutes in the morning when you get up ironically often helps you get to sleep at night. I used to read for 30-60 minutes every morning with breakfast to help me sleep. An electric blanket or simple heating pad helps many to sleep. Even if you are not cold the heat seems to make people drowsy. My wife uses that method.
Some other things to consider are lack of exercise and activity, and chronic sub-clinical pain. You can test for the pain by taking aspirin or acetaminophen/paracetamol before retiring at night. Just try it for a couple nights, and if you sleep better, it is likely that you are suffering from some low-level of pain that you don't consciously notice but is enough to keep you awake.
Also, sometimes the extended-release form of melatonin works better than standard. Eliminate any unnecessary stress form your life if you can. Some people also have used pyridoxine (Vitamin B6) for sleep as well, although I haven't tried that.