Once, i had a file that went very very big after an simple operation ( i was working with vertex ) , slowing down Carrara a lot . I took the previous save i had done and the file stayed little after that . If your file takes a few megaoctets although it is simple, then it could be the same problem . I hope you got a few saves of your work . If you don't, you could try to export your objects one by one, then reimport them in a new file . I hope that helps you .