Help!

What do you do when you have left a relationship and your starting a new one and find out your pregnant? Is it the ex's baby or the guy your starting the new relationship with? Problem is ex wants a child. New relationship does not as he already has three. What to do? Over three weeks late sick everyday and affraid to test! Any advice is helpful. Im a mom of three but feel like I'm in denial. IDK....again help or advice appreciated!