What can cause a month baby boy to stretching body and fats. Once he fats he won't stretch again??
They will stretch a lot particularly after a long sleep. When  baby is stretching they are helping all their muscles and joints work and function,  and as you've probably noticed also helping pass gas and even push out their poo.

I always use 2 guidelines to judge whether your baby's stretching is normal.
Guideline 1 - They are happy and contented when they stretch.

Guideline 2 - If they are unhappy and cry out they do this for a very short time. 

Even if your baby's stretches last a long time and are very frequent that's absolutely fine provided they are happy or they are just grunting  or groaning a little. Pulling faces is also fine as long as it passes quickly and baby doesn't seem upset. 
Is this the answer sir/ma?