Blood in Urine

I had blood in my urine pretty badly for about 2 and a half days and then it stopped. It was accompanied by a stomach ache and slight diarrhea. I went to L&D at the hospital first to check on the baby, everything was fine and my UTI check came back ok. It was really bad 2 days ago so I called my obgyn who did another culture and it came back negative. They did the 72 hour urinalysis.

Even though it is gone I am still freaking out my ObGyn said if it happens again they will send me to a urologist but for now just monitor it. I am so terrified it is cancer or something. Has anyone had this happen and it just went away with no explanation. I was peeing a lot of blood for a day. Like my pee was completely red. It is fine for now though. Any reassurance would help.