missmissy,
your issue is not strange to new bf mothers. The pain is due to the baby's latch. Even if the latch is correct, it's common for the nipples to be tender and sore, to the extent of cracked and bleeding - thus the pink BM. The pain near the armpits are likely due to engorgement. These symptoms will cease as time passes and your milk supply stablises.
Continue with the nipple shield if it helps with pain relief.
From my experience, I find the nipple shield helps my #1 NB to latch better as my nipples are flat, but they don't work to minimise the pain during latching. I used the shield only a few times as I prefer to do without the shield and just bear the pain, taking each day, each feeding as it comes and soon (maybe not THAT soon) bf is not an agony anymore. For my #2, NB latches on beautifully. Still, I experience some tenderness and engorgement during the first 2 weeks or so.
Hope you find motivation to hang in there!