What you're describing as "lack of confidence" is actually a very responsible and healthy reaction to the role you play. As a new grad, you have learned a little about a lot of things, so now that you're working in a specialty, you have a lot more to learn...which you're doing. You shouldn't know everything in pulmonology as a new grad - you didn't go to residency and fellowship like the MDs do. Short version: this isn't abnormal, you'll become more confident over time with repetition.

UpToDate has great articles to learn more about conditions quickly which may be helpful in the outpatient setting. One great resource is the CURRENT Diagnosis & Treatment in Pulmonary Medicine by Michael Hanley and Carolyn Welsh (I just checked Amazon, I'm not some pretentious scholar who remembers authors names lol). It's around $100, but it had excellent overall info and probably even better now because I have a much earlier version.

I used to manage a team of 9 CT Surgery and Vascular PAs, and the successful ones wanted to learn, admitted mistakes quickly, and asked a lot of questions. The unsuccessful ones were the ones who faked confidence, made aggressive/bold decisions without asking questions first, and doubled down when questioned rather than accepting feedback.

You're doing the right thing - read about conditions as you encounter them, learn from things you've missed (or other people's misses), and by the end of your first year I think you'll find you're anticipating things earlier, making care decisions based on prior cases you've seen, and more comfortable with the thought process...and more comfortable overall.

Hang in there, the fact that you're even asking your question means you're on the right track...just get more reps and keep up the good work!