hI THERE DEEPA. tHIS IS A CLASSICAL DESCRIPtion of a 'sebaceous cyst' or a 'wen'. Yes in most instances a cheesy material should pop out but perhaps this is larger & runs deeper than you think. It could also be just what you suggested..a 'blackhead'! Please go across to a dermatologist
in your area &/or a gen surgeon & have it looked at. It may need to be removed & is a very minor procedure done under local anaesthesia. Cheers & Good luck!
Dr Praveen Rodrigues MD Dermatologist & Cosmetologist, Vikram Hospital, Bengaluru, India