I’m having a medical thing and I’m hoping someone here can help me figure it out

On Sunday, I woke up with a really bad pain in my lower back and stomach on the right side. I went to the hospital because I thought it was appendicitis or kidney stones or something of that nature. All tests came back negative. Yesterday I was fine, not in any pain. Today I woke up with the same pain on my left side. It feels like period cramps in my stomach but my back also really hurts. I can’t sit or stand for long periods of time. I’m seeing my regular doctor tomorrow but I’m not sure if I can wait until then, I might have to go back to the hospital. Any idea of what this is or a similar experience, please let me know