What Causes Dark Bruise With White Circle In Center On Right Breast?

Hi, In May this year i had my gall bladder removed and approx 2/3wks later noticed what i thought was a bruise on side of right bust, it was pale pink, no lumps felt perfectly flat. Hv bn to my doctor and she examined and all seemed ok, but it is now darker and has a white circle in the centre. Overall size approx size of 50p. Should i be worried?