Tooth abrasion?

Recently I've noticed an increase in sensitivity on my teeth. Everytime I drink cold water, it is so sensitive. Im not sure whether it is a cavity or it is from me brushing my teeth too hard. Im pretty sure that my gum line has receded a tiny bit exposing a bit of my upper tooth, where it is very sensitive. Any opinions? I will be making an appointment tomorrow..and I can't seem to put my mind at ease. What can be done for tooth abrasions? Or even a cavity by the gumline.