Hello young fellow, I completely understand your deep concern for hyperpigmentation on neck and cheeks. In my view there can be multiple possibilities of the hyper-pigmentation including Lichen planus pigmentosus or Cautaenous amyloidosis or any related deep skin pigmentation issues. I suggest you to meet a dermatologist to get proper diagnosis of the condition by dermascopy or by skin biopsy. Do not apply hydroquinone repeatedly as self application. In my patients I guide them to use a broad spectrum sunscreen and certain safer creams containing kojic acid and arbutin. All the best.