I'd recommend:
Melatonin - Can be difficult to wake up from, depending on the individual. That is, can lead to grogginess the following morning.
Valerian - Smells like dirty socks, but it kicks a strong herbal punch. Go to sleep right after taking it though, I find if I stay up 30 mins afterwards, it loses it's effectiveness.
Chamomile tea or jasmine tea or even make your own tea using both. Jasmine makes for a very soothing cup, good for just calming down. There's quite a few herbs that lend themselves to calming, relaxing, and drowsiness that mix well and reinforce each other.
Meclizine - Actually for motion sickness, however has a very handy side effect of knocking you out. Useful pill.
Exercise - Put the energy to good use doing something constructive, plus the endorphins released put everything in a more positive light which just makes life seem better in general.
Meditation - Yes it sounds cheesy, but it helps slow your mind down which can be just what you need. Even 10 minutes can be extremely helpful. Try some of the YouTube channels that are full of ambient or nature sounds.
Yoga - Yes, yes, I know, more New Age shit, but it does help. Both Yoga and simply stretching can be admirably effective. Plus they have the added benefit of improving your dexterity. Stat training ftw.
Please be aware that herbs do still have side-effects and should not be used just willy-nilly. They may be all natural but so is belladonna, foxglove, and cyanide. Be careful, read up before taking anything, and ask first if you have any questions, whether online or in person. Certain herbs that are very useful, are also very potent; for instance something like St. John's Wort should not be taken if you have high blood pressure.
Also, make a pattern of using your bed only for sleeping (and obvious other recreational activities). Reading in bed, or doing work in bed can be extremely detrimental as then your body goes, "oh good I'm at the place where I do stuff. What do I need to do?"
If it keeps happening, I strongly recommend picking some new constructive thing to do. Whether that's a new work out routine, learning to paint, playing a new instrument, trying to learn a new language (I recommend
Duolingo), teaching yourself Python, carving wood objects, learning to cook, reading about a new science topic, hell even learning to change a car tire, it's all good and it's all useful. It especially helps if you are just generally feeling frustrated. Pick some new skill, give it a solid attempt, and then you can go, "ha! Look at what I can do now. I could not do that before but now I can. I have learned a cool new thing, and I am awesome for being able to do it. Check that out." Helps your self-confidence, gives you peace of mind, enables you to either know or be able to do something that you couldn't before, and just in general adds to the quality of your life. It's basically a win-win, that will also help you fall asleep.