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go to main menu, hit options, go to pregnancy category there should be an impregnation chance setting

When you were making your character did you take any of the perks when you got to the end of the character creator?  You might have accidently clicked the "infertile" or "no Hybrid" perks when making your character.

To check this go to the "skills menu" below the quick save button then go to the "skills tab" in that tab scroll to the bottom and click the "view base perks" button and it will show all if any perks taken during character creation.

Edit- If you didn't take any perks when making the character then the "view base perks" button will not show up.