Daughter having urgency to pee?!!

My daughter who is 6 has the constant urge to pee and sometimes she thinks she needs to go but doesn't or "can't" and she'll start crying because she tells me that she needs to go that her body is telling her but she can't ...the other day at Sam's club she made a huge scene wanting to go so bad but couldn't go this has been gong on for months I have told her doctor to check for UTI and everything came back negative and now it's getting worse..I'm on my way to the ER because I am frustrated and she is crying uncontrollably 😢 please pray for us! I feel so bad I can't do anything for her..what could it be??