If you think it is because of Teeth Grinding called as BRUXISM, you will also see eroded /kinda flat tooth surface and obviously your parents would have noticed it in these years.
It may be a TMJ(joint of your lower jaw to the skull) disorder. Apart from pain, do you hear any clicking sound on opening and closing your mouth?
According to what you have said, it may be a TMJ related pain but nothing can be said until you meet a doctor/dentist.
If your mom is sure about the NIGHT GRINDING thing, please meet your doc.
For temporary relief you can take some analgesics.