Thank you all for your advises. Know what? After some more days of having very "nice" nights, I realized that I was running too quickly to see him when he was just beginning to cry so, after being sure that he was warm, very good fed and all fine, one night I let him cry a little more and then he felt asleep again!!!! There was another kind of cry that night and I had to stop myself to not run to him and he continued sleeping after a few seconds! It was magic!
After that, he has been sleeping for all night again. Also, I wake up at 6h00 am and give him a full bottle and continue sleeping for two more hours.
Thanks again for your help.
Now I can say I am sleeping as a baby!
Bye