Ouch, you have my sympathies.
In the immediate term (ie when she does it) you could try (and it's hard, cos you want to do the opposite) pushing her head (nose in particular) towards your breast, as that generally makes a baby release her bite so she can take a breath!
4 months-ish is a notoriously fussy time - lots of brain development going on at a furious rate can disrupt behaviour in loads of ways - so gut reaction is that it is a phase and it will pass. Maybe she's learning cause and effect ?
It's hard with a very young baby to do anything behavioural, because a 17wk old is only just starting to compute the world in a way we'd understand as human (the neo-cortex kicks in at around 4 months), but just in case she's suddenly realised she can provoke an interesting reaction, you could also try keeping calm (ha! yes I know how nuts that sounds), saying something like 'biting' and putting her down immediately (according to experts you should first associate the word with the action, before adding 'no' to the front of it) and keep doing that until she gets the message that biting = feed over.
You could also try a nursing necklace or toy to keep her attention towards you but provide another game other than biting you!
Hope some of that helps. I remember 4 months as being a particularly trying time - my DD used to turn her head away to look at whatever was going on in the room, while still attached. I had no idea nipples could stretch that far .