I posted before I got to see your reply, Holly. It's really frustrating, and I'm sorry that your experiencing these problems, hun. BF is very natural, but it doesn't mean it comes easy, or that it's at all instinctive. Hang in there, you're doing really well to make the effort to work out what is happening, especially when you've been struggling with mastitis already.

If the white coating on your bub's tongue is not there anymore then it definitely will have been milk. With your nipple looking whitish straight after a feed (and especially if that goes away later too) that could be a sign of issues with your baby's latch and that your nipple is being compressed in bub's mouth the wrong way, affecting the blood flow, and causing the stinging. Does it hurt particularly badly when you feed him? Especially when he first gets attached? Does the white look to your nipple go away after some time? Is your nipple shape round or squeezed into a different shape when DS finishes feeding?

Your areola shrivelling sounds like it could be a vasospasm related thing?

Can you call the ABA helpline to ask for advice?