Re: Scared new mother needs some reassurance...
Welcome to the forum and congratulations on the new baby!
I don't think your anxiety should be off the scale. It sounds like you're doing wonderfully well, with maybe a few things that you could tweak but which your baby will probably grow out of with time.
If baby has plenty of diaper output and is gaining weight well, then it doesn't matter how much she spits up because there's plenty staying down in her tummy. Incidentally, babies spit not because they are overfed or because there's something wrong, but because the muscle sphincters which hold stomach contents down are weak in a young baby, just like all her other muscles. Time will take care of the spit-up issue, I promise! Until then, you only need to worry about spit-up if the baby is not gaining weight well, if the spit-up is literally projectile, and if the baby seems in pain when spitting. If you need reassurance about the amount your baby spits up, try pouring an oz of milk on your countertop. (Cow's milk, please, not yours!) You'll see that milk spread out like crazy, and it will look like a lot more than a single oz.
Some frustrating feedings are very normal at this point. You might want to try swaddling baby so that she can't push the breast with her little hands, and you also may want to try to latch her on before she's really hungry. Hungry babies get frantic and become difficult to latch. If you miss that "I'm hungry but not yet frantic" window, and baby is squalling and thrashing, try offering her your pinky finger to suck, with nail held down towards her tongue instead of up towards the delicate flesh of the palate. A few seconds of sucking on your finger might calm her and remind her that sucking is the solution to her distress.
Coughing during feeding is baby's way of protecting her airway, and it's a good thing when baby is able to do that. Swallowing and eating require a very complex series of muscle movements, and young babies are often a little uncoordinated in this department. But they get better at it! Often what is going on is that a young, small baby is struggling with a rapid milk flow. It can be like drinking from a firehose- the milk lets down and WHOOOOSHHHH! This is another problem that will improve with time, as your baby gets better able to control milk flow and your milk supply adjusts so that it's meeting baby's needs pretty exactly, ith out a lot left over to cause rapid letdowns.
The two things I'd really like you to do are one, to think about seeing a lactation consultant, preferably an IBCLC, for help with your latch, and two, to experiment with nursing without the shield from time to time. Eventually you're going to want to wean from that thing!
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"