What I can do to flatten/lighten my breast scars? (photo)

Thank you for your question. Breast incisions can be managed using a multimodal approach in the post-operative period:
1) Scar massage - starting as soon as the surgical dressings come off and the incisions are sealed
2) Silicone sheets or scar gels for about six months to year
3) Embrace - a tension reducing dressing for the first 2 months
4) Fractionated lasers to help blend the scar into the background - done as a series, starting about 4 weeks after surgery and repeated every four weeks for six months.
5) Sunscreen to prevent the scars from darkeningThis far out after surgery, I would recommend that you consider fractionated lasers.  With the darker skin tone, you may want to consider a radiofrequency procedure such as the Venus Viva.  I would also consider the use of steroids to help reduce the degree of scarring.  

The 1540 fractional erbium laser can reduce pigment and flatten hypertrophic scars.  You will need at least for treatment scheduled a month apart.  Final results and improvement will be seen at 6 months to 12 months.  Steroid injections while they will reduce hypertrophic scars often cause fat atrophy which causes the scars to sink in and widen.

You have hypertrophic scars. These can be treated with steroid injections, but bear in mind that they are not 100% successful and they have some local side effects that your doctor should warn you about. They are not the same steroids that can affect your body as a whole in any way, so you need not worry about that. They can help to soften and flatten the scars. However, the scars themselves are permanent and I trust you were appropriately informed of this prior to your surgery.