Whats stitch in side?

Fold in the pleura. This is a knife-like pain that happens from time to time to many of us and taht gets worse as we breathe in. There are many myths, but what is actually happening is that the pleura folds on itself, like underwear might do. A very deep breath will generally end this, or it will self-cure. It's almost never related to disease and if you have no other symptoms, ignore it.