You could be lacking in iron, best way to tell is probably see the doctor you'll probably have a blood test to check you iron levels.
Maybe try eating some foods with good levels of iron in it such as:
Lean red meats, including beef, pork, lamb.
Seafood, such as oysters, clams, tuna, salmon, and shrimp, etc.
Beans, including kidney, lima, navy, black, pinto, soy beans, and lentils.
Iron fortified whole grains, including cereals, breads, rice, and pasta.
Greens, including collard greens, kale, mustard greens, spinach, and turnip greens.
Vegetables, including broccoli, swiss chard, asparagus, parsley, watercress, brussel sprouts.
Chicken and turkey.
Give these a try hoefully they might help.
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