We just bought our first pig. She's a little over 2 yrs old, a hamp/york and is due 9/23. She's had two litters with 12 to 15 piglets each time. She delivered and raised them with no problems. So we brought her home to a nice big pen with a elect wire around the bottom and a shelter with a bale of straw, food and water. We tucked her in bed, kissed her goodnight and went inside. That night we had a tremendous rain storm with thunder and lightening. In the morning she was gone! She stayed gone for four days except for a couple of sneaky visits to her food and water. We finally caught her at the trough and slammed the gate. Boy was she mad! She rushed the fence, tried to climb over, broke the hot wire and generally scared the bejeebers out of us. Finally after a couple of days she's calmed down. But she's thinner than when she went on her little walk-about. Do you think she's lost her babies? How can we tell? Is there any special feed for a skinny (maybe) pregnant sow? Thanks for listening to all this!
As far as the pregnancy you might look for the signs Walter reported on here: Pregnancy Indicator As for the poor eating and inactivity, she might just be depressed and lonely. If she came from a farm with lots of pigs and now finds herself all alone she might need some attention or entertainment. Throw a soccer ball in her pen, scratch her back with a stick.
I would agree with Milo. She is in a strange land with strange people. There is a period of readjustment. If she is due 9/23 then I sincerely doubt she farrowed since she would only be about half way through her pregnancy at this point. If she's do that far out she won't be showing a lot of belly yet.
It is possible that the due date is wrong.
Is she bagged up? If she did farrow then she'll be bagged. That is to say her breasts will be large and full.
Were her breasts clean around the nipple? That would be a sign of nursing.