Terminated from first nursing job.... not really sure where I went wrong

I was let go from my first nursing job and was really caught off guard by it. I was told that I was eligible for rehire with May grads. I did not feel as if things were going great, but I certainly didn't think it was headed down this road either. I began working in NSICU and after 4 weeks (without any previous meetings or updates) I was told by my ANM that there were concerns -- for example, my preceptor said that I did not give good report, that my assessments were not thorough, and that I took too long giving meds. I was really blind-sided by this and I asked my ANM how come my preceptor didn't say anything to me. In my mind I just thought, oh my goodness, she has been watching me fail and not saying a word. I told him that I did struggle a bit at first with giving report until I developed a form that worked well for me so I wouldn't forget things, I was still learning with doing assessments but I was charting on this information; so again how come nobody said anything to me. He seemed a little surprised that I was not aware of these issues and he said he was going to follow up with my preceptor and the educator. He also asked me if I had thought about med-surg or progressive units, and I said no because I had been working in ICU and I thought that was going okay. Nevertheless, the next day he and the educator terminated my employment stating that I was not where I needed to be and that they thought I should first work on med-surg or progressive. They said that they looked throughout different departments but there were not any current openings for new grads (and there are not, the job market is terrible in this area right now for new grads) so I can interview with May grads..... I was completely devastated wondering absolutely what happened. What did I do to screw up and wondering how I can improve. What makes it so bad, is that I called the ANM a couple days afterwards and I left a message (hoping maybe to get some tips and pointers on what I can do differently in the future) and I did not get a call back. My job search is going okay I guess, but I am hoping some experienced nurses can help me make sense from this. I really want to learn from this experience and move on in a positive way.... but maybe I am reading into it too much and I am just not ready for ICU and just need to start in Med-Surg.... I welcome any thoughts, ideas, or suggestions..