It may be tightness in your quadratus lumborum, if it’s a pain that’s more specific to one side of the low back than the other (thought both sides can be irritated). That muscle often gets very tight in people who do lost of twisting motions or sit in a chair often.
You mention forwards and backwards stretches, but not side to side. Try these if the pain is one sided, and stretch to the side away from the pain. However, when I do this stretch, I have my extended leg more out to the side (like a half-splits) and grip my foot with the overhead-hand, to lengthen the stretch along my sides. I will also tuck my elbow and forarm of the lower arm against the length of my inner thigh.
Does that description make sense? If the twisting motion hurts, of course, skip trying this tretch and seek a physical therapist or professional. Same if both sides are tight and hurt… it’s hard to stretch one side to get relief if the other side is shortened, pinched, compressed, etc.