thanks for asking your query.
your back pain
needs special investigation. because even after getting sitting with osteopath its not improving instead getting bad. so you should get x-ray done for your back- (x ray
LS SPINE- AP & lat view). if the x- ray comes out normal then it must be some muscular problem with your spinal extensors (weakness, spasms) so you can take the help of a physiotherapist. Or if it shows something else then your treatment has to be done accordingly.
wish you good health