Been evedrywhere else nobody knows

Patient: I have been experiencing a lot of low back pain… for starters if I stand up wrong or sit too long and go to stand my low low back, almost butt area, will lock up on the left side and it causes me to fal. I am 25 and I have beared 3 children. I am not overweight. Second about 5 hours into sleep every night I will wake up due to what feels like tight compression around my spine in my middle back, causing it to be very hard to breathe or even move. I can void sometimes but it doesn’t help the pain, after about an hour or so of being up and moving the pain will subside a little. Do you know anything that can cause these symptoms? My x ray and mri of lower lumbar showed normal but obviously its not.