You say nothing is bothering you — except something clearly is. But it may not be mental. If you haven’t already, the first thing you should do is see your medical doctor. There are a number of medical conditions that can make people feel this way. The thyroid is often the culprit. A vitamin deficiency is another guess. It may also have something to do with your sleep or nutrition. See your doctor for a thorough check-up.
If you are physically fine, ask your doctor for information about where you might find free or reduced fee mental health support. Then go for an evaluation. Let the counselor know your financial limits and make the best use you can of however many sessions you can afford. Sometimes all it takes is a few sessions to jump start a new direction.
In the meantime, I hope you are taking care of yourself. That means eating a healthy diet, getting at least 7 – 8 hours of sleep a night, staying away from pixels in the hour before sleep and getting a good cardio-vascular workout a few times a week. It’s really true that the key to a healthy mind and attitude is often in a healthy body.
I wish you well.