Lower Back Pain, Right Side

So I started to experience this very frustrating, sharp lower back pain on the right side of my back. The first time it happened was three weeks or so ago, when I was doing leg curls, last legs exercise after hard workout. I was already tired and used too much weight and I think I pulled the muscle. But the thing is that it doesn’t hur at all most of the time. If the muscle was strained or pulled, I think it should always hurt and especially when doing exercises.

Right now I started Jim Wendlers workout - The “Boring But Big” 3-Month Challenge.
For example I can do Deadlifts for 3x5 with heavy weights just fine, then I go to do squats with low weight for 5x10 and I still can do fine, but around 4th or 5th set, the pain comes back. The pain is really sharp and it’s not my spine or anything, I can clearly feel its the muscle or some nerve on the right side of my lower back. It’s painful to even walk back home, but after I get back and lay down for 10mins up to hour, my back is completely fine again.

Also when I did 3x5 squats with heavy weight, I was still feeling good, but then I did first set of 5x10 Deadlifts with light weight and pain got really bad, so I had to stop my workout and go home. So it’s really frustrating, I took off last week from any kind of workout and started stretching in the mornings now, but I still did get the pain yesterday after doing squats 5x10.
Does anyone have any idea what could this be and how to deal with it?

Could be nerve or SI joint issues and very well could be due to something muscular but if I were you I would speak with a sports therapist or chiropractor if u have insurance or can afford it and in the meantime keep your weights low enough to not cause pain. It has been a year since I herniated a disc in my back and I am just finally getting to the point where I can start squatting with the bar again and working my way up. Listen to your body, I did not and paid for it.