Right Rib Pain After Appendicitis.

I am 24 years old, male. It all started with appendicitis(it was a gangrenous appendicitis with peritonitis). I got it removed 4 months ago, but 10 days after I was released home that strange pain appeared... I was making ultrasound and blood tests each 2 weeks after the operation, and they were normal. I also had 2 x-rays done in those 4 months(nothing was found).

The first whole month this pain was only appearing after I made a deep breath. It was under my lower right rib(on the front side) next month it moved to the right, and then a little closer to my back. This pain is very small. It don't bothers me(maybe only a little) or anything but I am just interested what could be causing it. And this pain is connected with breathing and moving. After it moved closer to my back it stopped hurting when I breath in, but it started hurting when I breath out and relax my muscles at the same time. What's interesting is that it don't hurts at all when my lungs are full of air. But when they are empty it hurts to move or walk. Each step I make causes a small pain(but it's probably because when you are walking you are making some movements with your torso too). There is no pain when I am laying down, and there's allmost no pain when I sit. The pain only appears when I am standing. The highest pain is when I breath out, standing, and relax my muscles at the same time. I can't describe the pain itself... It's a combination of sharp and dull pains. It's located somewhere on the back/right side of my lower ribs(on the right side of the rib cage). When I kick that part with my hand it hurts too.
The pain is not located too deep, but it's not on the skin either.

If someone here knows what it is, please help me! Thanks in advance!