Hi Eelco, welcome to DB!
You've come to the right place with your diving questions.
First, do not despair too quickly.
Many people do not know how to equalise properly, and do not know the various ways to get those tubes open, clear and flexible.
The best thing is to learn these things in person with a skilled diving buddy, freedivers are by far the best to learn from.
Fist you say you can get down to 3m with pain in your ears. This means you're not far away from diving at all because it means that your sinuses are open!
Ok, let's hand you a very basic online course.
Preparation:
1) Be healthy.
2) Sleep well.
3) Drink extra water, avoid sugar, milk and other mucus inducing foods.
4) Take hot shower, and have hot water warm your forhead, and gently tap and rub so you warm up and loosen up your Eustachian tubes.
5) Tilt your head a bit up, hold 1 nosehole close with your thumb, and inhale, snort up all the mucus that is coming loose. Do both sides.
6) Enjoy the cleared fresh hollows in your head.
Let's learn the most basic equalisation technique, called Valsava.
The goal of equalisation is to increase the air pressure in your ear and sinuses to counter the mounting water pressure on the outside of the ear and sinuses. Practice on land first. Venturing into new terrain, always go slow and gentle. If uncertain, stop and ask.
Equalisation using valsava:
Be sure to have done the preparation, if your head is congested, have that clear up first before you equalise or go diving.
Equalisation pushes air into the ears, and if they're blocked, or nearly blocked, you push the dirty mucus further in creating more problems and possibly infections.
1) Stand in front of a mirror, and close and hold your nose with your index and thumb.
2) Close the mouth and gently push the air from the lungs to your nose as you holding it. Because you've got your mouth and nose shut the air goes to your sinuses and ears if your forehead airways are open. You may hear and feel a pop. You can see the pressure push the nose out, if you hold it by the end. As your ears 'pop', you may feel the eardrum moving. You've just done your first Valsava Equalisation. Congratulations.
Practice, and improve your technique so you need very little force to equalise. Your tubes and muscles will get more flexible and it all will become easy. In the beginning it may take more effort, and your 'ears' may get tired after a number of repetitions. Just take a rest, hydrate, and always make sure you keep your ears: Clean, Dry and Warm. That's why may divers wear diving caps.
In the pool.
When you got the technique down on land, lets test it in the pool, it's best and most fun to have a buddy.
1) Put on a mask (with nosepeace).
2) Go the shallow end.
3) Equalise above water with the mask on, test if it works just as well as at home.
4) If it works, you can decent feet first by exhaling a bit and holding on the pool ladder, Equalise gently every feet or more you go deeper.
5) If your equalisation does not happen, halt and give it another go, if it still does not work go back up. At the surface you can use the clearing methods listed in the preparation part above. Be gentle, focus on relaxing the face and tongue and using technique.
5) You did a good job if your hear do not feel any water pressure at all.
The above was going down feet first or head up. After this try being horizontal, or even head down equalisation. These can be more difficult to do.
1) Equalise above the surface.
2) As you keep holding your nose, also keep the pressure up and duck dive down to the shallow end.
3) You'll find that when equalised and swimming at the same depth or ascend you do not need to equalise.
4) See if it works for you to the deep end.
When you want to swim deeper you need to equalise more. When you swim down gradually you'll need less frequent equalisations, when you go vertical you need a lot.
When you start to dive deeper faster, you may encounter you on your way failed an equalisation and start to feel the pressure on your ears, now you're behind on your equalisation. Now equalisation becomes really hard to do, and soon your ears can stretch no more and you'll have to turn or bust your eardrums. - Which is very disorientating and painful.
Valsava is a very crude base technique with drawbacks. Those include people blowing in and obstructing their ears and sinuses, creating blocks, causing damage and or disease. Also some people manage to blow out their own eardrums because they apply way too much force. - This is why I wrote be gentle and sensible, and ask if in doubt.
Do a search on equalising techniques and learn the other more advanced techniques that we freedivers use to reach to impossible depths.
Let us know how you go!
ps. feel free to tell us more about your life and passions.