ive had my pot beely pig to vet for blood in urine.. he has no urinary track infection or stones . what could be wrong .. there is alot of blood .when he goes.

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Age: <1; Male; Breed: pot belly pig

Already Tried:
took to vet . they gave him amox. for urinary trank infection . he stil,l has blood more so then when i took him. and today they told me he doesnt have a urinary infection or stone. they took a xray.