. I hope you are not taking any medicines because fixed drug eruption causing hyperpigmented skin is very common with certain medicine. Hyperpigmentation is darkening of the skin. This darkening occurs when an excess of melanin, the brown pigment that produces normal skin color, forms deposits in the skin.
I suggest you to get this possibility evaluated from your doctor.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.