Cain & Abel?

In the Bible (Genesis), after Cain had killed his brother Abel, Cain was stranded across the earth, and he had to survive on his own. So, he built a city named Enoch (after having a son named Enoch). Which comes to the question, who was the wife of Cain is the only people were Adam, Eve, and Cain (since Cain had killed Abel)? Where did this other woman come from? Did God make more people? Or did Adam and Eve have more children not mentioned in the Bible?