I have really bad tooth ache in my back teeth, please can someone tell what will help with the pain?

A dentist. It depends on what is causing the pain. If it is decay, you can try clove oil until you see a dentist. If it is an abscess you need an antibiotic. If it is a fracture usually just not using the tooth will help.
Need treatment. Dental treatment would be necessary no matter what. Short term relief with over the counter pain meds is possible.