My 4-month-old has started causing me a lot of pain while she's eating. She latches on fine and starts eating right away. But then she puts one of her palms against my chest and the other against my side and straightens her arms while she's eating. This causes her to pull on my nipple until she pulls it right out of her mouth. Then she latches right back on and proceeds to push herself away from me again. I've tried holding her hand so that she can't push against me, but I haven't found a way to control the other arm. Does anybody have any ideas about why she might be doing this and what I can do?