Back & Flank - Help Please!

Not sure if I posted in the right spot in the forum - but I'd appreciate any one who could help.

Two months ago, I had stomach pains, accompanied by a fever, that made me go to the doctor.
He said it was an acid issue and prescribed me to some antacid pills.  I took a blood test and everything came back negative.  

After about a week, all stomach issues disappeared, but some other issues developed.  
Almost simultaneously with my stomach issues, I've had some flank issues.
I would feel a dull pain on one side of my body, in between my lowest rib and my hip.
The pain doesn't get severe, I can still do normal daily activities and play sports and all.
However, the dull pain is there, at certain times of the day I'll forget about it, but for the most part, persistent throughout the day.
The interesting thing is that the pain switches sides.  One day, it'll be my right side.  The next day, my right side would feel normal but same symptoms appea on my left side.  
Never have both sides had that dull feeling at the same time.
A third symptom would also sometimes appear - mid to lower back pain.
Again, if back pain appeared, it would be on its own - the two sides would feel normal.  
Then the next day, one of the two sides would get that dull feeling again, and my back feels normal.
The back pain is a little worse than the side pain - just feels like a sore back from lifting something heavy.
I can still endure it and exercise and all, but if it's there it's worse in terms of intensity than the side issues.

Anyone know what this could mean?  I don't go to the doctor because I'm not ill at all - no fevers, nausea, sudden weight loss, nothing like that.
I've been browsing around and seen it could be kidney but I'm not sure if that's the right location because my dull pains are exactly in between the lower rib and hip.  I would imagine the kidney is a little higher up but I may be wrong.  But again, I never feel sick - no blood in urine or anything like that either.
Just three symptoms of dull pain (left side, back, right side), that switch off daily and stay persistent throughout the day but never occur at the same time.

Thoughts?  Thanks in advance.