I asked because all your symptoms fit malnutrition and over-exercising and even prescription drugs can cause that. A lot of people unknowingly skip meals or avoid higher calorie foods that can easily put them under the amount of calories a person need in a day.
Have you ever calculated how many calories you're averaging a day? It's worth your while to at least eliminate calorie-restriction as a possible cause.
A good free and easy app to help calculate your nutrition: