When did you first notice the brown patches?
Are you breast feeding?
I would look for some 100% pure emu oil and use it as a moisturizer on these spots, as well as looking for a good efa supplement to take internally such as hempseed oil.
I've heard this is quite normal for pregnant and postpartum women, it's probably got something to do with horomones. I always got a brown line from belly button to pubic area - very annoying. But after pregnancy it would get dry and flake off like dry skin from a sunburn. Weird!
Anyway, pregnancy can effect everyone differently, and almost always it's all considered normal and part of the process.