Dear friend,thank you for your consultation.as you have told us that you used to have back pain before you bumped your back I must assume you have some chronic back pain problem.see ,back problem can be of various types.but most commonly it is because of weakness or straining of back muscles around vertebra.so if you start doing regular physiotherapy like doing flexion exercise it will give you some relief.also please dont lift heavy weight or bend forward too much.in this way you can give your back muscles a rest.and now I am telling you that the lump and the bruise you got can be due to swelling caused by that bump.so please do regular antiseptic dressing and take some broad-spectrum antibiotic to control local infection.putting hot water bag on that lump will help to decrease the swelling.thank you.