what is this pain?

Ever time I've peed since two days ago I have gotten a pain in my lower right abdomen. It starts sharp and then turns into a dull pain that kind of radiates into my upper thigh and lasts for awhile. I took an AZO UTI test and it comes back positive for leukocytes but negative for nitrile. I'm not really sure what his could be. I was kinda thinking UTI or kidney infection but this test kinda tells me no. I do have an IUD so I was kind of worried about perforation, but it's been over a month with no problem. I do have my 1-month ultrasound next week to make sure it's still in place. Does anyone have an idea of what this could be?