I feel like i need to go to the toilet to poo but when i do, nothing come out, sometime just gas and maybe a very small piece of stool. what can it be?

Tenesmus: That feeling of having to go, but nothing comes out is called tenesmus. It can be from inflammation in the rectum, something called proctitis. Sometimes this just happens once without a definite explanation. Or it could be a sign of longer-term issues of bowel inflammation that are starting. If you have fevers, bloody stools, worsening pain, see a doctor.