DD1 only bit me once accidentally very young and my shriek and leap from the couch scared her witless and she never did it again.

DD2 started doing more what you're talking about at around the same age. In her case, it was when she was done with a feed and I was persisting (so hard to tell with this one, she only ever feeds for a max of 5 mins, from birth). I needed to pay more attention to the signs that she was done and def not try to reoffer if she spat the bb out! Fortunately, she's also a sensitive soul, so when she does it and I yelp she gets so upset she cries and my bb is at least free.

Hope this stops for you soon.