I had a friend who picked up some sweet almond oil too after hearing that I was trying it.
He says he has felt sore in his lower back too. He is used to working pretty hard and injuring himself, so he never thought the two were related.
Before this, he was taking olive oil, and I was taking walnut oil. I'm not sure what would be acting as an irritant; I thought it was the oleic acid, but since he used to take olive oil and seemed fine with that, I'm not so sure. Then again, if you don't think of a possible connection between the oil and the back pain, you'd keep taking it and think the pain is from something else.
Is anyone on olive oil experiencing lower back pain?