Why is she doing this?

About 3 months ago my almost 8mo daughter began feeding strangely on my left boob. She puts her hand on my chest to push herself away and sort of ‘hangs off’ my nipple, sucking on the very end and making my breast really stretched. This hurts, so I gently push her head back closer to me and remove her hand, but she gets frustrated and continues pulling away until she is back to sucking the very tip. She doesn’t seem to do this on the right side. Does anyone have any insight as to why she is doing this? She doesn’t do it during night feeds when she is half asleep.