What Causes Vaginal Pain With Swollen Labia?

I've been having pain/discomfort around vaginal area for past week. It's gotten worse today and only bothered me when I sat, now I feel it when I walk. My period just ended and at first I thought it had to do with that, but like I said it's gotten worse. I noticed that left labia is swollen (at the bottom part). I'm having an mri done tomorrow for other reasons, would it be able to pick up whatever this is? (Mri is of lower abdomen/pelvic region)