Situation is not very clear by description. U need to see a good dentist soon. They will evaluate your problem though a full mouth X-ray (opg) and examine all your teeth.
Next Steps
Your problem could be because of rigorous and faulty brushing technique. U need to check that. Brush with a soft toothbrush and in up and down motion. Not horizontal. Don't brush for more than 2-3 mins twice a day.
Health Tips
U can use a desensitising toothpaste till proper treatment is done.