And just to keep the story short, after consulting a friend, a vet herself, she advised me to check his teeth again and gave me a good reference.
So that good referenced vet came to see my horses teeth and surprise surprise!, bad job done last time! And I had already asked the "butcher" to come check them again and he said they were fine.
So, teeth "done" again this evening, let's hope for the best.
Oh, he has a lot of blisters in the back of his mouth, outside his molars. :(
So it's mouthwash to take care of it and lots off grass!