BODYBUILDING: Back Head Pain When Lifting Heavy?

Ive been experiencing sever back head pain below my ear on the left side when i lift weights in the gym lately. The pain usualy lasts between 30-1minute and then leaves me with a mild headache the whole day in that area. It is so frustrating because i want to continue my bodybuilding program but i cant because the pain is so intense. Does anyone know what and why i am getting this? i drink plenty of water, and eat 1 hour before training, i dont smoke im 19 and eat very healthy. I do not take any suppliments.