Fired

I had a shitty morning, I started working as a vet assistant at the end of January and this is my first job in the veterinary field. I was hired and was supposed to be learning on the job how to do everything, I thought I was doing pretty well at it and everything was fine, last week my boss told me I was doing great and was fitting in well. Then this morning after I got there she fired me because "I didn't fit in with the team". No one ever told me that I wasn't doing well and I don't know what I did wrong, I asked why and she said "we seem to always have assign you work to do", I have been here for a month and I'm new at this and learning so what was I supposed to do? It doesn't make sense to me to fire someone who is new at their job a month in and still trying to grasp everything that is going on, and I feel like I didn't get the chance. She was really vague with her reasons and I don't understand what went wrong and I'm not on a probation period. I'm really sad about this and I have an interview tomorrow with a different clinic and I don't know what to say when they ask why I was fired. I'm completely floored because this was the last thing I was expecting and cried the whole drive home. Any advice helps, I don't know what to say or how to feel and I'm so embarrassed.