I had this problem a few years back, brown patches at the sides of my mouth and on my chin which made my quite self conscious, it also became worse during pregnancy. I used a cream called Fadeout from Boots, its about Ł8 a pot. I think it works by gradually absorbing the increased melanin which is near to the surface of the skin giving rise to the brown patches. Now would be a good time to start as it takes approx 6 weeks of regular use to make a difference, you would also need to use the cream or a sun block in the sun to prevent and limit your exposure to the sun. It is very mild doesn;t smell very nice but does moisturise and contain vit e. Its worth a try my brown patches have gone, it may be worth asking a pharmacist for any ideas, or whether there are stronger preparations than the one in Boots, perhaps a beatician would be able to help or the advice of a dermatologist if it is really bothering you