Why can't I sleep even though I'm tired?

Online Answer
If you're tired but can't sleep, it may be a sign that your circadian rhythm is off. However, being tired all day and awake at night can also be caused by poor napping habits, anxiety, depression, caffeine consumption, blue light from devices, sleep disorders, and even diet.
Related Questions 📌
Melatonin is the hormone released by your brain to make you feel either sleepy at night time or awake during the day. When it's dark, melatonin is slowly released, telling your body it's time to go to sleep. Being around too much bright light before bed can affect the level of melatonin that is released.
One of the simplest explanations is that it could be due to your body requiring more rest than the average person. However, it is also likely that your tiredness is due to the lack of quality sleep at night, rather than the quantity of it..
When you eat too much of something, it's no longer rewarding to you (this not only applies when you eat too much in one sitting, but also when you eat the same food too many times - your brain is hardwired to find novelty more rewarding than something it has already experienced)..
Coffee itself won't instantly make you feel tired, but the caffeine it contains may actually lead to fatigue after regularly drinking it over time. If you stick to 400 mg of caffeine per day or less and go easy on the added sugar, you should reap the benefits of caffeine and avoid its drawbacks.
The Mayo Clinic lists several medical conditions that could be behind your exhaustion including: anemia (iron deficiency), heart disease, diabetes, thyroid problems and others. Even allergies, vitamin D deficiency, or the medications you're taking could be making you tired.