I sleep better after yoga, but I agree it's not an instant fix. Melatonin doesn't work for me, but I suspect I haven't tried a large enough dose. If you do try it, you might do a bit of research on dosage and timing. I have used Benadryl during some phases where I've had trouble staying asleep. It won't keep me from waking up, but it makes it easier to fall back asleep.
Longterm, you might look into meditation or more fully commit to a regular yoga practice. I know you've struggled with insomnia and excess stress in the past. It may benefit you to explore some new avenues for stress relief. I know exercise helps, but it sounds like it might not be enough.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher