Ultrasound showed kidney stone. X-ray didn’t. Have a lot of pain and test shows blood in pee. Is there a stone or not?

If a kidney. stone is tiny or doesn't have a high enough calcium content, or if it is obscured on xray due to superimposed bowel contents or other structures, it is possible that it would only be visible on US and not xray. A CT scan would be more definitive when there is a discrepancy.