Brown vaginal discharge, odor, pain/itch?

[a ¡long! way ¿down?]

My period ended Sat/Sun, and ever since I've had a light brown discharge with a distinct odor, accompanied by pain and itching in that area. The discharge is watery and slight but still smells strongly. I only used 1 tampon during this last period and definitely took it out, so it's not that. I'm only 15, far from sexually active, and would really rather not have to tell my mom about this, since, you know, it's embarrassing. So if all you have to say is "see a doctor," I'm probably not gonna follow your advice, sorry. Also, this probably isn't related, but just in case, yesterday I began to feel slightly nauseous, light-headed, cold/hot when no one else was, and had a headache. I came home from school and slept (waking up for periods of about fifteen minutes sporadically) til 10:45, when I went into the bathroom and started to wretch but never threw up. I think that may have been dehydration? Anyways... sorry for the gory details. Beyond dehydration, any idea what this is?