Pain in right side/back/flank area. Had X-ray, what now?

[pltmh93]

For about a week now, I've been having a dull-crampy (3 out of 10) pain in the right side of my abdomen and back area.

The first day, it came on relatively suddenly while I was sitting at my computer desk. Being the worry-wort that I am, I immediately thought it was appendicitis, but I decided to wait a few hours just be sure, the pain didn't get any worse or better, so I went to bed and told myself that if it's not worse by tomorrow morning, it's probably not appendicitis, and in fact I woke up the next day and the pain was gone until I started going about my day and the pain seemed to come back with daily activities.

I became concerned again, thinking now it may have been a kidney infection and decided to check myself into the urgent care. They took a urine sample, blood work, and did an X-ray of my lower right abdomen, they said everything  looked normal, and the sent me home.

6 days later, the pain still comes and goes, and overtime I've discovered that the pain never seems to stay in the same place. While most of the time it remains confined to around my right hip in the flank area (especially in my back), I've also felt the pain in my upper right abdomen about where the last rib in the rib cage is, occasionally in my mid back, occasionally near my belly button area, and even occasionally in my left flank area.

Pain is my only symptom. I'm passing stool okay, no pain or burning with urination, no blood in my stool or urine (that I can tell anyway), no nausea, vomiting, or diarrhea, although I believe I was mildly constipated within this time.

What I'd like to know is what exactly could be seen on my X-ray? What would the doctor be looking for? Because my big concern now is a tumor or cancer of some type. If this were the case, would it show up on my X-ray or in my blood and/or urine? And being as they told me everything looked normal, do I have any reason the be concerned that the pain is continuing?

I'm 22 years old, slim and don't have the best diet (consisting of a lot of fast food, microwavables, and soda). I drink occasionally, but never to the point of getting drunk, always just one or two, I have smoked marijuana, but never done any other drug, and I'm not taking any new medications or anything.

Please help, thank you!