Lower left rib pain in pregnancy?

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Hey ladies, just wondering if anybody else has had an almost constant aching pain in their lower ribs? And what was causing it?
I'm 28 weeks tomorrow and the pain is on my left side and seems to go all the way from the front left to the back left. It's usually fine first thing in the morning, but within an hour of waking up it's there and lasts pretty much all day. It's manageable, just an annoying, dull ache. I did think it felt similar to a kidney infection I had a year or two ago, but I've not had any symptoms of a UTI this pregnancy that could have turned into a kidney infection. Any thoughts??
I should probably add I have a midwife appointment in two days and I plan to ask about this, but thought I'd get other womens' opinions beforehand (: