Dear Beata,
I did not have this specific situation, but from 1 to about 2 and a half, my son's speech was quite garbled and unclear, even for his age. He also had recurrent ear infections. At that point, I consulted with a naturopathic physician about a problem with his digestion, and she told that milk protein intolerances cause chronic congestion in young children, including in the ear canal. I got my son off ALL dairy, including in baked goods, prepared foods, etc., and it was like bam -- his speech just took off. He literally learned 50 new words in a week. Today, at 3.5, he has such a big vocabulary that we've had people in stores, etc., stop what they're doing and stare in amazement, I swear.
So, to me, an earwax buildup sounds like a red flag for a milk protein (or possibly another dietary) intolerance. You might try getting your son off all dairy (and this means reading every ingredient label). I also really recommend consulting with a naturopath or a holistic nutritionist -- the standard battery of allergy tests won't catch this.
Best wishes,
Mira