Upper back pain

I’m no stranger to back pain but this week has been brutal, upper back spasm up to my neck and down to paraspinal muscles, the muscles feel like thick cords when i massage them, i did a lot of weight training off and on, and currently im off, i’ve been carrying a backpack to work (both straps) but it cant be more than 5kg, so why would it affect me this much? And how do i relieve this pain? I’ve tried heat and cold, ibuprofen and stretching.