There have been times in all of our lives where we had to learn something the tough way, OP is now learning the hard way. Yes, should have had the dog fixed, that's covered, now let's try to be helpful.
First thing you need to work on, pregnant or not, is the running out the door. Regardless of how long she stays gone, it is never good to let a dog (especially a pit) to just take off. Your dog or someone's kid are very likely to get very hurt. And if she IS pregnant, she could injured and lose the pups and possibly her own life.
Until you know for sure if she's pregnant, try to keep her calm, no rough housing, and give her good food, some carrots and peas and stuff.
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