I am just starting in an ICU, and I had basically the same experience. Three months off of orientation, I was called into my manager's office and taken by storm about how other people have shared multiple concerns about me. I broke down and couldn't finish the day at work. They asked me if I wanted to go back on orientation, shadow with another nurse, etc. She asked me if ICU was right for me- and yep, that's what really got me. I thought I was doing okay, progressing, making some friends on the unit slowly... But this meeting contained no positive feedback, whatsoever.
I met with my manager and the assistant manager the next day, to recap about the previous meeting and talk about what could be done. I requested this meeting. I intended just to talk about what could be done moving forward, but spent more time trying to defend myself and wrap my head around the situation. I could have handled the whole situation a lot better. We decided the manager will shadow me and my patients and assess where I need help.
You shouldn't have discouraged yourself like that. Maybe that was your biggest mistake. Yes, your orientation seems to be unfair, with so much inconsistency (one preceptor telling you you're doing great/ no feedback, and another telling you that you suck). I was also on basically only nights for my entire 3-month orientation. Maybe 5 day shifts throughout. I definitely lack in my admission, discharge, going-to-tests, and contacting providers and families skills because of that. Okay- THAT'S A LOT OF THINGS! This is my first job, and starting in the ICU is like being thrown right into the pot. You have to sink or swim. Honestly, maybe you weren't ready, but don't continue to discourage yourself now!!! Just because you weren't ready doesn't mean you can't do GREAT on another floor in the hospital.
My advice to you is to get a job on a step-down floor or something where the patients are a bit less sick and there's a bit less pressure. You'll make better money here than the clinic. You have about 6 months of ICU experience to offer them! You'll do great. Hone your skills and build your confidence, then maybe you can reconsider ICU in a bit of time. The hospital can be a very cutthroat place, and sometimes no one is in your corner but you. Don't let that corner be COMPLETELY empty.
I'm no expert, this is an accumulation of advice I've gotten, mixed with my hopes and theories about how to grow in this profession. Just because I didn't lose my job this week doesn't mean it's I won't. I have 6 months left on my contract. A the end of the day, you probably did a lot of things right, too. You just have to have faith in yourself.