How to get rid of unwanted hyperpigmentation caused by co2 ebrium laser? (photos)

i had co2 ebrium laser two years ago for treatment of old stretch marks. After initial treatment i had a lot of dark brown spots on the back of my legs and the buttock area. 19 months in of using obagi and tretonoin i still have discolouration. The spots have got lighter but are still there. On my left leg i have a big patch of reddish/white blotches, looks like 'cornbeef skin', and have dark red patches that have seemed to taken up home in the tracks of my stretch marks on my right.