I had all the same reasons. If I got up at 10 in the morning, then at 12 I could hardly stand up. And he slept whenever possible - but very restlessly. This is most likely a consequence of prolonged stress. But when you cross a certain border, the body can no longer recover from a permanent failure. It sounds strange - but after many years of torment, a course of injections of magnesium and calcium helped me (in my opinion). The point is that when the syringe and when in the ass is more effective. (With the registration of a doctor!)
In any case, you need to see a doctor. Find a specialist in your condition, and do not just donate blood for analysis - he will most likely be good and you seem to be healthy. But the condition you described is very unsafe. And most importantly, it will no longer be possible to just sleep / wait out. The bad news is that if you do nothing, it will only get thinner. The good news is that it can be fixed with medication. fast and cheap. But any actions only with the hand of a doctor.
In fact, there are many reasons. I will list, as I like, according to the list.
1.1. Lack of thyroid hormones is perhaps the top cause of asthenia.
1.2. Any of the anemias.
1.3. Low blood pressure, hypotension is not life threatening, but greatly reduces its quality.
1.4 Depression, although with this disease almost always, a person either sleeps very little, or vice versa.
2.1 Sleep apnea
2.2 Sleeping too little or too much.
In general, the most likely and correct choice is to go to a therapist and complain about chronic drowsiness. Let him look for a problem.
Most likely, this is just chronic stress.
Many people, with great mental or emotional stress, constantly want to sleep. At the same time, sleep is enough for a short time or they wake up already tired.
Coffee helps a little, but do not overdo it. First of all, you should think about your lifestyle and attitude towards it.