Hi Geir ,
The english word you are looking for is Sciatica , it is usually caused by one of the discs in your back pressing on the sciatic nerve , causing pain in the lower back which spreads down the legs. I really feel for you , as I have a similar problem ,except mines is in the neck. Pain killers help , especially the ones that come in green bottles , I think the medical name is Heineken.:cheers: