Why are there egg whites over my yolk when I try to make a sunny side up fried egg?
I suspect that you are using fresher eggs and are cooking too hot or too long. 

In an egg, there are two different kinds of whites, the outer, runnier, and the inner, which clings more firmly to the yolk.

If you crack a fresh egg and place it on a plate or in a pan, you can see a distinct “bulge” of egg white. This also means that there’s a thicker layer of egg white on top of the yolk. 

When you cook your fried egg via the steaming method described in the question, this layer will coagulate and become opaque. Even in older eggs the effect can be noticeable, but it’s more pronounced in fresher eggs.

To prevent this, you need to leave the layer of egg white slightly undercooked - that means lowering the heat in the pan to generate less steam and to carefully cook until the main part of the whites is just done, leaving the yolk runny. If you want a more done yolk, you have to rely on bottom heat alone, so that the yolk acts as insulation for the white on top, which means leaving the lid off.