Mine did that too.
I know this seems counterintuitive, but as soon as I felt her start to clamp down I pulled her much closer, so she had to detach herself to breathe, then I would offer her something she could bite on. And explain that mama is for milk and love, and her bumblebee teething ring was for biting.
Perhaps yours is starting to teethe or is learning what to do with teeth that are in there. Mine was using her gums on me - darn those baby jaws are strong!
It took a couple times, but she got the idea, and it wasn't too scary for her or hard on me.