I noticed a small protruding skin, like a big pimple, in my pelvis, what could this be? do i need to see a gynecologist or dermatologist?

Skin: Either. Any primary care doctor or a dermatologist would work. Simple skin problems are easily addressed.

Depends: It depends on where it is exactly. If it is on the vulva or near the rectum, i would have you see a gynecologist. If it is more on the legs or abdomen, i would see a dermatologist. Although really, both will probably be able to help you. Good luck!