Answers provided are for informational use only and don't confer patient-provider relationship. My name isXXXXX and I will do whatever I can to help you.
Dr. Saha has given you some excellent possibilities. However, none of them (thyroid, sleep apnea, electrolyte imbalance, anemias, hormone imbalance, etc.) can be detected or eliminated without testing with a primary care provider to determine what the problem is. Blood tests (CBC, metabolic panel, thyroid panel) would be the very minimum required.
Since you don't have insurance, I would suggest you try one of the free clinics. There is a list below, but you will probably find others in your local telephone directory since not all local clinics make the national lists. The clinic where I volunteer weekly isn't on the national list, for instance, although we see thousands of patients per year. These clinics are staffed by providers who volunteer their time from their regular practices to see patients who could not otherwise afford medical care. They often have some specialists who they can refer patients to if the diagnosis is a complicated one after routine lab tests are done. The specialists work with the patients to make care affordable if it isn't pro bono.
Actually, a lot of people will become sleepy when bored with routine tasks. There are also things like reactive hypoglycemia (low blood sugar) that can make one feel tired and inattentive an hour or so after a high starch meal. The solution for that one is to divide your diet into 5-6 small meals a day, each containing protein so you don't have this. Most people associate hypoglycemia with a diabetic who has had too much insulin or not enough food, but people without diabetes can have reactive hypoglycemia that they completely control by what they eat and when. For instance, a salad with some chicken for fish is a better lunch for a hypoglycemic than a sandwich or pasta. When you get hungry later in the afternoon, a peanut butter cracker or some non-fat yogurt are better choices than a candy bar or a soda. These are changes you can make that require no testing at all. A brisk walk around the hallway every couple of hours may also keep you more alert and attentive. In fact, that is something recommended for anyone doing repetitive work.
Please let me know if you have questions.