In spanish do you put a y after a comma?

In a list of items you do not put a comma. However if you use it as a coordinating conjunction you do.

Example: I ate Oranges, Apples, and bananas this week.

Yo comí naranjas, manzanas y bananas esta semana.

Martha carried all the light packages, and Sam carried all the heavy ones.

Martha cargo todos los paquetes livianos, y Sam cargo todo los pesados.