You are definitely not alone with those feelings. I think it's pretty normal for new grads to feel overwhelmed and doubt themselves in the first year. Being on night shift probably has a lot to do with your irritability...I was on night shift for two years and felt depressed most of the time. My body was confused about when it should sleep and eat. When you mess with your body's basic human needs, it messes with your mental functioning....I too felt the feelings you described but though it was "normal" to feel that way on night shift. I recently got a job on days and my whole physical and mental being is a complete turn around. Some people just aren't made for night shift and that's okay! Hang in there.