I get back pain every once in awhile and it tends to linger for 1-4 weeks. Then it goes away for a month or two.

I try to work my abs and lower back, as well as stretch my hamstrings.

As for sitting up straight, I think the most recent guidance is that a 120-135 degree thigh-to-back angle is optimal: http://news.bbc.co.uk/2/hi/health/6187080.stm