Try a soft mattress. It has now apparently immerged that they are more beneficial than the traditional 'hard mattress' cure for bad backs, which is really not good for an injured back as the weight is not dispersed evenly. I hurt my back and suddenly found that my average mattress was now torturing my back, and it eased when I got a soft mattress. If possible, get one of those special foam ones that mould to your back.
For a few months you should take better care- ensure your back is well supported with a padded upright chair when sitting, try not to slouch, don't carry heavy things as this can put a strain on the neck with the 'pull' of a bag, never mind the actual weight of something.
You could try chiropractors. They manipulate the bones back into shape and take x-rays to look at misalignment. I'm no doctor but it could be worth having private physio as he may have meant that it was, to be crude, not worth the NHS paying for you to have it as your back may not be bad enough for their criteria, but it doesn't mean that physio can't help you, if you see what i mean. Get your parents to pay for some sessions (£35 ish each) if neccessary, but I would try all you can.