Blasphemy
First off, nice gains man. You're obviously learning what it takes to put on weight, you look good man. You'll be at 170 in no time. I'm also guessing this pain is from rows/deadlifting and probably results from your increase in the weight you're lifting and form that's not 100% correct. It happens.
I'd take at least a week off back bro and do stretches for it. Your body is probably coping with the additional mass and stress that it isn't used too. Just google back stretches where you're getting the pain and do those 2-3x a week while laying off the weight. The last thing you want to do right now is keep pulling heavy weight, especially if you're deadlifting. Back pain blows and you'll save yourself a lot of headache if you just lay off it for a little bit until your body feels "right".
Once your back loosens up and it starts to feel "right" i'd take the weight down a little and just practice strict form and higher rep ranges until you feel like you've really got a handle on things. Taurine can also help with back pumps during workout days, I've always gotten them like a mofo so 10g before back/leg days is basically a staple for me.