At 5 months in you're still getting into the flow of things, especially as a new grad. You feel like you're getting there, then a patient throws something at you that makes you feel totally incompetent, right? It happens all the time. I've been on my unit not for 15 months and still have days like that. I think everyone does. It's not because you're incompetent, it's because you haven't seen that particular thing yet. No shame.
It takes awhile to fine tune that critical thinking side, but you're probably already doing it at least subconsciously. And never worry about asking questions. The only dumb question is one not asked.
Good luck!
Tom