Your expression regarding sadness of mood unrelated to circumstances, and unreactive to environment around you is highly suggestive of a ongoing depressive episode. The negative feeings , crying, preference of solitude etc. all point toward same direction. My strong suggestion to you is to seek medical help at the earliest. You should seek a consultation with a psychiatrist, who will diagnose your condition correctly, rule out medical causes, and provide you with treatment. Treatment would consist of medication and psychotherapy as is necessary for your health. It is important for you to known that depression is a treatable health condition which is quite common. Seek help early to avoid complications. Hope this helps you, wishing you an early recovery...