Apart from that, avoid sitting or bending forward for as long as you can't bend backwards.
Once you can bend backwards, stretching can help, but gently.
get a bit angry with other people. (haha, see my story)
More seriously, lie on your stomach on the floor and gently lift yourself up on your arms (like a pushup) only leaving your legs on the floor. This gets the curve back into your back in the right spot. It is considered first aid for lower back problems.
get a big exercise ball and stretch your back on it...
those fancy *** mattresses.
That's stress. Find out what's bothering you and deal with it
New shoes? Visit a chiropractor? Go swim laps?