I don't know about the bump, but I'm pretty sure it's normal for your skin to be darker in the areas you describe. I don't know what you can do about it. Personally, I would just leave it alone. If it's causing you embarrassment for some reason then see a dermatologist and see what they advise.
I'm also pretty sure it's normal up to certain point for the skin to be some how darker in certain areas. But the difference in me goes from very fair to very dark brown and it was not always like that.
The dermatologist will be the last option since I am not really eager to show my very, very private parts to a dermatologist, unless is absolutely no choice.
How about your gynecologist? You should be getting a PAP regularly, and your GYN would certainly be the one with the answer. As for the cream, that is kind of strong to be using in such a delicate area and it really won't do much good for lightening the skin in that area since it works on the epidermis layer of skin not the dermis. What you are describing is normal coloring as most women have dark skin in the pubic/genital area. The bump could be an ingrown hair or cyst. Again, check with your GYN doctor to be safe.
I agree with the others, what you describe sounds normal :-)
I saw a program on TV (I think the Style network) in which women were paying to get their skin bleached.
Have you noticed this at all under your arms or back of your neck? This happened to my daughter and I called her dermatologist. They told me to take her to an endocrinologist. I did. It is due to metobolic disorders. I'm having a brain freeze or I would tell you the name of what she has.