Hi Filipe, it sounds like we have similar experience (and experiences) of diving. I found that I was getting similar symptoms to yours, and in fact I got a couple of ear infections which were no fun at all.
It seems I was getting reverse blocks: I wasn’t equalising very well while descending, so that my eustacian tube would become a little inflamed and would become clogged with mucus.
Two things have really improved the situation for me.
Firstly, I saw a doctor with an ear nose and throat specialism and she suggested using a neti pot to clear my sinuses occasionally (I always use it before diving). It seems to help. While I was recovering from the ear infection she prescribed decongestants and anti-inflammatories. I also found it helped to wiggle my jaw from time to time.
Secondly, and most importantly, I have really concentrated on my equalisation technique. I am taking a breath for every metre I descend, and on each breath I use the valsalva manoeuvre. I also wiggle my jaw and tilt my head a lot.
At first I had been frightened of blowing too forcefully and damaging my ear drums, so that in fact I was not blowing hard enough to equalise. It has taken about 20 dives to get familiar with the technique. I usually go diving with a local dive shop team and they make a point of letting me start my descent before their other guests so that I don’t feel any pressure to rush my descent. That makes a big difference. I’m still quite slow at descending but I am getting a little quicker, and I no longer have any ear problems.