X-ray suggests decay in second molar tooth. As you are complaining of acute pain, it suggests decay has reached pulp causing inflammation and pain.
RCT is basically removal of inflamed and infected pulp from the decayed tooth.
Next Steps
Go for RCT for 7 as your dentist is suggesting. After RCT your dentist will fill the cavity with permanent cement and then you might require a Cap on it.
Health Tips
Don't delay it. Medications will give you temporary relief.