I am sufering from in digestion from last 4 years please tell me why

Diet maybe.
Other than that I'm out of ideas from the small amount of information given.

What tests has your doctor done? What has your doctor suggested? Has you doctor told you what the issues are?

Have you seen a doctor?

That's really your only option. We can guess, but that's all we can do. A guess isn't a diagnosis, and only a diagnosis will help you get to the bottom of this.

We can't tell you why, only your doctor can do that. You may have to adjust your diet or possibly take medication to control it.