Stronger bread, how could I achieve that?

Gluten is a protein that gives bread elasticity. Water makes gluten spirals relax, and kneading helps stretch the gluten and connect with other gluten strands. Bread that lacks stretchiness:

• may not have enough gluten to start with. If you are using a low gluten flour then you won't get and elasticity. In general any plain white flour will have enough, but for best results use bread flour, also known as strong flour
• may be too dry. Gluten needs water to relax and stretch, if your dough is too dry, or "tight", then you won't get good elasticity
• may have not been worked enough or worked in the wrong way. Kneading mechanically stretches gluten, if it isn't kneaded enough, or the technique isn't right, then no elasticity
• may not have been risen enough. Yeast actually improves the dough, it really works on the gluten. Rise isn't just about leavening, it makes a big difference in elasticity. You should notice a big difference if it's been risen enough

If I had to put money on it I'd say it's probably your dough being too dry. This is an easy mistake to make, you turn your dough out on the counter and it's really gooey, must not have enough flour right? But as gluten get worked it uses up some of the extra moisture, so adding too much flour at the beginning will rob the gluten of the water it needs to relax. Kneading with oil instead of flour may help there.

As an aside, I generally add a couple of tablespoons of olive oil to my pizza dough to improve flavor and texture although that's totally optional. Also, you didn't list salt as an ingredient, bread needs some salt, many bakers recommend 10g per 500g of flour, although I usually cut that down some.

GdD's information and suggestions are all informative and helpful.

You might also try adding an 'autolyse' rest as the French do. After mixing the water, yeast, and flour together until well combined, allow the dough to rest for about 20 minutes. This allows the flour to become hydrated and the gluten to start its development. Since the gluten begins to develop as soon as the flour and water join, less kneading is required after the autolyse rest to develop the gluten. After the autolyse sprinkle the salt over the dough and knead until the dough is smooth ( a baby's butt is a apt descriptor here) and elastic. Adjust the liquid by teaspoons and flour by tablespoons to achieve the desired texture. Knead until it feels smooth and the dough feels like the texture of an ear lobe when pinched. Stretch a small piece of dough to test elasticity. If it can be stretched thinly enough that it is translucent and light can be seen through it without tearing, it has passed the 'windowpane test' and the gluten is adequately developed and elastic. The bread should have adequate structure.

Forgetting to add the salt after the autolyse will hamper the gluten's development as GdD implied. If this is a concern, the salt can be added to the dough initially. My experience has been that an autolyse with a dough containing salt still helps the dough's gluten develop more quickly. And there is not the risk of forgetting the salt.

In the U.S. bread flour usually contains a small amount of ascorbic acid (vitamin C) which helps yeast multiply and gluten develop. It can be added if not already contained in the flour, about 1/32 tsp. per 3 cups of flour is commonly recommended.