MY 85 YEAR OLD FATHER IN LAW HAS BEEN HAVING

MY 85 YEAR OLD FATHER IN LAW HAS BEEN HAVING PAIN OFF AND ON RIGHT SIDE OF ABDOMEN FOR COUPLE WEEKS. HAD XRAYS YESTERDAY TO CHECK FOR CRACKED RIB. THEY SAID LOOKED NORMAL. TONIGHT HIS PAIN HAS BEEN MORE CONSTANT. HE JUST HAD BLODD WORK DONE MID DECEMBER AND EVERYTHING LOOKED GOOD. LIVER SEEMED FINE. WHAT TESTS SHOULD HE BE GETTING? ULTRASOUND NEXT? MRI?? HE IS STUBBORN AND SUGGESTED THE ER OR WALK IN TOMORROW DEPENDING UPON PAIN LEVELS.