On my head, i have small blotch that is light & spreading slowly. in the center there is a red bruise that appears, scabs, disappears, ?

Get it checked.: Could be a skin cancer (basal cell or squamous cell carcinoma), or even a melanoma. Or it could be a benign lesion. Impossible to tell without looking at it directly. Have a dermatologist look at it at your earliest convenience.

Dermatologist: Lesions that a=asymmetric, b=irregular boarders, c=irregular color pattern, d=larger then the size of a pencil eraser are worrisome. If your fit the abcd rule, have it biopsied.