Question about pregnant piggie

Question
Hello.  We adopted our mom-daughter pair the first week of January from a pet shop.  Long story short, when the sow started to look pear-shaped, we called the pet shop and found out a male had been in with her for a couple of weeks before they discovered their mistake.  Oops..not good!  But we are prepared for babies and are looking forward to it.  But here is what I'm puzzled about:

We estimated the latest due date being about March 7th or 8th..so that is coming up, obviously.  And although she is very pear-shaped..she has never gotten huge like many photos I've seen. The lower portion of her belly has become very round, firm, and heavy.  I know this is hard without a photo...but some of the pregnant sow photos I've seen are shocking because the sow looks so miserable.  Whereas our sow looks noticeably large..but smaller in comparison to the average photo..if that makes sense!

Next thing that seems different than the books is the fetal movement.  In the books, it says that you should be able to feel the skeletal structure of the babies and actually hear their teeth grinding. Well..I'm not hearing or feeling this.  I'm feeling bumps and vibrations..but that is it.   So, I suppose my concern is that everything is so subtle compared to what the books say.  There is definately a pregnancy happening...but perhaps this is what a one-baby litter looks like?  

Thanks for any info you can offer.  I just want to be prepared in the next week or so.

Whitney

Answer
First thing first, make sure they are both females, don't count on what the pet store told you.
www.cavyspirit.com/sexing.htm

What you are describing sounds like a perfectly normal pregnancy. All sows are different sizes depending on their litter size. In the last few days she will blow up like a blimp in what seems like a blink of an eye.
www.guinealynx.info

Make sure your cage is big enough
www.cavycages.com