From your symptoms it looks like nevus of ota which is usually congenital but may be acquired and found in adults also. The other possibilities are melasma which is caused due to hormonal changes in body, actinic lentigo or phytophotodermatitis.
I suggest you to get it evaluated from a dermatologist to confirm the diagnosis. Biopsy skin may be needed to confirm the diagnosis.
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 dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.