Painful boob

Hi there, so I have had a painful boob (L) for the last few days, I am on a contraceptive and usually both boobs hurt for a couple of days after my injection but I’m not due another injection for two weeks and it’s never usually one. I’ve checked it and no lumps or changes it’s just a little swollen and sore to touch! Getting a bit concerned about it now :/ has anyone else experienced this?