Thank you for your reply. I have consulted a GP, he says can't tell anything at the moment until conduct a test, which is the same solution as yours. He suggested watch it and get tested if any significant changes. From a one and half month period, its size become smaller, say 20%.
Also, I am quite sure it is not a foreign body, and it is right under the horny layer, not in front of the skin.
A reasonable guess is that this could be a black pigment or something produced by my body internally. Or may be a reflection of my recent lifestyle (sleep very late, final year study rush). Will that be an indication of weak immune system? Cheers.
It can be a small splinter or foreign body which got embedded but not infected or it can be a small freckle. The other serious possibility which has to be ruled out is of a melanoma. I suggest you to get it evaluated from a dermatologist. Although the probability of this spot being melanoma is very less but it has to be confirmed by examination first.
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.