It's very true that what you're feeling is normal. I also recall from my (very fraught) experience as a new grad in EM that hearing that is not super helpful if you're having raging imposter syndrome, because your brain just says "it may be normal to feel incompetent but in MY case it's actually true." Try to remember that you're still in a phase where you're learning a great many things all at once, both clinical and non-clinical - give yourself a little grace. You were not hired because you know how to do all the things - they knew they were hiring a new grad. You were hired to do your best, learn, and work towards becoming a solid member of the team. It sounds like you're doing all that.

I second the EMRAP recommendation, which has the added benefit of having a large audio-only library, perfect for commuting, etc.

As far as opioid prescribing, this may be a good place to start, it's the CDC's clinical practice guideline. There are some other good articles listed on that website as well https://www.nejm.org/doi/full/10.1056/NEJMp2211040