Fear of separation/going to a new school

My child is 6 years old and I have been seeing that she is having difficulty coping with a new set up. It all started when we changed her school 2 years ago. For initial 4 days she didnt have any problem. But after that she would wake up in the night or early in the morning crying not to send her to school. We tried dropping her off in the school bus. As soon as she saw the bus she would cling on to me or complain of stomach ache. Just the thought of the school would make her anxious. We did spk to the staff but couldn't come up with the actual cause. After trying for 2 weeks we gave up and put her back in her old school. She never had any issues with her previous school earlier. But after this incident she experienced the same fear when she saw the school gate. Thanks to the supportive teachers she enjoyed her schoolng. We recently moved to another city and now trying to put her to a summer camp to which her friends also are going. But she refused to go and starts crying