I am 23 years old. I played volleyball in college for 3 years and all throughout highschool. I also play basketball on a team outside of school. Coming out of high school was where I began to take my workouts more seriously. I went from a skinny kid to a slender man but then I started noticing my left mid to lower back muscle started getting bigger than my right muscle. It never caused me any pain. The physical therapist and athletic trainers at my college told me there was nothing to worry about as this is normal with athletes, especially volleyball players due to the repetitive spiking motion of a single arm. I took a break from working out for about 6 months before I graduated due to laziness. I started working out again in May of 2016. After a few weeks of getting back to what I was lifting before, I decided to push myself much harder. I increased my squat and deadlifts by a good amount. My back muscle got a little bigger than before. But now I have an aching dull pain in my left back muscle only when I sit for too long. I never have pain while lying down or play sports. And progressively it has been getting worse. I am unable to sit for longer than 30 mins without the pain beginning to rise. The longer I sit the worst it gets. I was examined by an orthopedic surgeon and he said I may have very minor sclerosis but he cannot be sure. Xray showed no structural defect in the spine, only a small curvature of my spine due to my enlarged muscle constantly pulling on it. I am getting an MRI soon. We are pretty sure this is a muscle problem. I recently bought a roller and that has been helping.

TLDR: left mid-lower back muscle is a lot bigger than my right. Pain only when sitting too long. Most likely just a muscle problem.

Does anyone else have this problem and have any advice or solutions?

nothing to worry about my dude
that agonizing pain is just weakness leaving your body

Experienced a similar problem.
With me it was my hip flexors being thight as fuck.
Started stretching out my lower back and hip flexors, problem solved.

Also, what's your focus on core in comparison to lifting? I mean, I do ab excersizes 3 times a weak, and 2 back workouts per week.

don't sit too long

Possibly left muscle is compensating for weakness in other areas of body? Possibly hamstrings, hips, core maybe?

you played volleyball, that's your problem

Honestly man, consider throwing some yoga into your routine. I would get strange injuries like this and I could use a roller for temporary relief, but nothing else has helped more than a SOLID stretch. Hope you start feeling better!

One of the few terrible troll still remaining here

What happened to that alpha male deathslayer or some shit