Love my new car but my back is broke!

fineso.mom

Hi lads, I hope someone can help.
I just bought a vauxhall astra 2010. I drove it on a few short journeys the first few days and all was good. Then I drove to Dublin from Limerick. ....the pain!! After about an hour my back started to hurt, I tried moving the seat, the steering wheel, nothing helped. The return journey was the same, my back was killing me after half an hour.
Since then, even short journeys are uncomfortable.
I've never had this problem before in a car and when I sat into the car first day the seat felt great, like it was supporting all of me. I'm a 5ft7in woman,so not very tall or very short.
Anyone any ideas what I can do?
The seat only has manual adjustment. .forward/back, up /down and the back goes forward and back. There's no lumbar support adjustment.
Also it's the older model astra, I think there was a new one in 2010 but mine is the same as 2009s.
Thanks.

orm0nd

would a back support be any use ?