Hello,
Your teeth seem to have localised periodontitis. However a better look with radiographic and oral examination can confirm the diagnosis.
Next Steps
You must immediately opt for an ultrasonic scaling by a dental professional. Expect some minor bleeding while the procedure is done, rest assured it is normal. Post scaling, kindly avoid having extreme hot or cold beverages for a few days.
Health Tips
I'll advised some topical antibacterial and anaesthetic ointment for a few days to relief the pain further.
Also, the stains on your teeth signify tobacco abuse. Would advised to quit chewing any form of tobacco/ pan masala.
Good luck!