Kidney pain in pregnancy?

I went to the ER a week ago after waking up to an extreme pain in my back, where your kidney is. They didn’t see anything in an ultrasound but I had blood in my urine. It’s been a week and I haven’t experienced that degree of pain again, but i have this persistent dull pain that kinda comes and goes in waves. I went in for a follow up with my OB yesterday, no blood in urine and scheduled another ultrasound in a week. I am still having these waves of discomfort and I’m wondering if anyone has experienced something similar? It’s only to my right side, no pain peeing... it’s just a mystery at this point