Yesterday I stopped and took a deep breath. Ok I'm learning new songs and feel like I made some progression since last week but something was not right. I could not find a good position for my left hand and was moving it all the time. Thumb higher, lower etc. My fingers felt cramped, the tension in the hand was high. So I search and watched tutorials and compared videos and pictures.

I realized my position was very wrong and probably the reason why my hand was hurting. As you can see in the next picture, the weight of the violin is half supported by the hand who is pinching it for stability.

Now this make playing with the 4th finger very difficult and it's also hard to press the strings vertically (was pressing them a bit diagonally).

With my revised position, who still need work of course, my violin weight is supported by neck/shoulder and stability by the meaty pad of the thumb who is now lower. That allows my fingers to reach higher and drop down on the strings vertically. 4th finger is a bit easier now, but every bit counts right? Tension is gone the hand feels free, the fingers unlocked. Anyway, I'm happy and look forward to improve it until it's great.