sudden pains-spread from left to right side of lower back.

Hi there, I'm a 22 year old girl from England. I got diagnosed with IBS (mixed) when I was 17 after going through a lot of stress. My IBS is normally well managed and I haven't had many severe attacks for a while now. Recently though for no apparent reason I've been getting a sudden pain in the lower back which starts near my right kidney and spreads across to my left kidney. Sometimes its only in my back, but it can also spread through my stomach too. It comes on quite fast, not instantaneous because I can sense when it's about to happen and it's a really unusual pain, not like normal IBS pain. it feels almost sore, like tender, and it feels funny when I breathe in too deep. Normally it lasts about 10 minutes and will just disappear and I'm fine again. It really alarms me and when it's at it's worst its awful. I should also probably point out that its not really a stabbing pain, more of an ache, like I said it's tender and my breathing feels 'sore'-which I know probably doesn't make any sense really.
Does anyone else with IBS have this problem or know of any related illnesses? I seriously can't find any info on the internet relating to it, only stuff which implies certain kidney diseases which I'm not sure it'll be, and it's not so easy for me to get a doctor's appointment, plus I often find that doctor's here are very dismissive with IBS sufferers because it's such a common illness in this country :-/
Thank you for any help!

Hey thankyou, I get a lot of stomach cramps, but because they're often after eating meals I put it down to my dinner triggering my IBS, I never really thought it could be anything else because I'm pretty healthy considering I have Ibs :) I don't really understand what you mean by UC too I'm sorry :s. It's kinda similar to period pains I guess yet not quite, but at the same time I just can't explain the feeling properly, I've never experienced anything else like it :s I just spoke to my mum and she said it sounds like a spasm, but it's not a griping pain, it's just intense and spreads like a wave over my lower back/ occasionally stomach. Can you take this budenofalk for ibs too, what does it actually do? I think maybe I should see my doctor, something's been niggling away in my mind for a few years now, when I was younger I had a load of bloods taken to test for intolerances, and the nurse told my mother that I had an abnormality relating to my liver, but it was nothing serious and I shouldn't worry, I wonder if I should worry now!