Hi thanks for writing here.Dermaroller
treatment casuse damage to scarred tissue,from epidermis
,dermis ,and collagen
.It is done in multiple sittings and depth of damage is increased in every sitting. Since it is your third sitting it is possible that this time your depth of damage is increased,also after every sitting there is oozing of pinpoint bleeding ,considering all these things it is always possible that there is some sort of post traumatic hyperpigmentation
,which is common,and it will recover within few weeks,continue with melawash and kojic cream,take sunprotection ,You can also apply a mild steroid
like desowen for few days which will give you faster results.Take care.