Hi!
Sensitivity can be due to decay or if there is attrition( removal of the top layer of the tooth)
If minor, as you addressed ( teeth looking normal) can be corrected using desensitizing paste.
Few cavities won't be visible as the one saucer shaped just near the gums, when the tooth surface worns out due to mastication/ night grinding habit - these won't show any signs of decay.
Next Steps
Visit a dentist for clinical consultation. It won't cost much- just the consultation one.
Health Tips
Brush with soft bristles.
Don't brush too hard and for long time ( 2 mins brushing is enough)
Use desensitizing paste.
Sensitivity of the tooth is the stage where still preventive measures can be taken with less cost concern. Take care.