Hi,
This seems to be arthritis of the temporomandibular joint on the right side, the joint capsule is damaged because of which it is getting stretched while you open the mouth widely as well the pain over the front of head is due to muscle strain caused.You can take pain relievers (such as Ibuprofen/
Diclofenac), can apply pain relieving
gel over the joint and do gentle massage for 3-5min. Avoid chewing hard food on the affected side, take only soft feeds.