She used to be fairly intent and placated by feeding (she's 6 months now). About two weeks ago she started squirming around quite a bit while drinking from her bottle. She arches her back and moves all over the place. She's still happy and hungry, I just can't figure out why the change from calm to a total wiggle-worm would have taken place. Thanks!
That's what's great about parenting. As soon as you start getting it down, it changes. It's a stage every child goes through. As they gain more control over their bodies, they assert it. Try some different holds until you find one that works. I've found two different ones useful. One is to cradle the baby in my left arm, but hold the baby's right arm under my left armpit, so he's turned a little more toward me and is restrained from turning. The other way is to sit the baby on your lap facing out. It looks weird, but works really well for some kids.
My daughter(6months old) does the same thing: she's very squirmy - will take a few sips, stop to look around, take a few more, stop and so on. I try to give her a blankie so she can feel the texture and although this sometimes helps, the only time she will peacefully drink her bottle is in the night time.
Mine does this too. I hate to be the harbinger of bad news, but it only gets worse. Your baby is only going to get more mobile, more energetic, smarter, able to see and process more, and therefore more interested in the world. By the time my baby was 10 months old, she would take a few sips from her bottle, sit up, look around, lay down and take a few more sips, and lather, rinse, repeat.
What helped was giving my baby her lovie or another piece of cloth, blanket, or toy with interesting textures to hold while eating. It doesn't work all the time, and it has worked less and less as she's gotten older, but at 6 months it helped a lot. You'll have to determine if your baby prefers consistency or is better when looking at/touching a different toy/texture each feed. It ran in stages for my baby. Good luck!