Hello..the pain in forehead is a referred pain from Upper teeth due the nerve plexus being interconnected . The pain on chewing could be probably due to decay, infection in upper tooth.the constant pain is a sign of acute infection.
Next Steps
you need to be seen by a dentist to get a clear idea about the clinical picture by proper diagnosis through x- rays.the tooth infection can be treated through root canal treatment thereafter.
Health Tips
1.keep your teeth line & gums free of bacterial plaque by constant rinses with warm saline water.
2. you can have over the counter painkillers to manage pain and discomfort
3.avoid chewing hard stuffs from the affected side until you get it treated.