Been there done that waited too long, road too may times and ended up in Surgery L4/L5 fusion.
Dude, Do not mess around with that crap, Stretches and all of that are a great start. Don’t be pounding down a huge Dh at 30 MPH and expect your back to feel great. Your best bet it to take some time off the rough stuff and HEAL.
I did not heed the advice above and got to where I couldn’t walk, I had surgery and was flat on my back AND off work for three months. It took me almost 6 months before I could ride anything again and two years before I felt like I could trash a trail like the old days.
You should go have an MRI and see whats really going on if you have not already.
Good luck and BE Careful with those back issues.