Rigid and tender abdomen, help!?

What can cause a hard abdomen thats tender but not caused by pregnancy or constipation? I did see a doc a few days ago for UTI symptoms but they were negative. she felt my abdomen. It was rigid bellow my belly on and my right side was kinda lumpy and tender. She put me on antibiotics but didn't order any tests. Its been three days. I still have intermittent flank pain and abdominal pain. I don't have a fever.