Keep objects (without hierarchy)... saved my day! Thanks everyone!
My last file was 260MB very, very large, and when I made new small changes the file jumped to 600MB and then I saved as again and then jump to 1.250GB! no chance to work on it.. Now, after File -> New -> Keep objects (without hierarchy) the the file is 32 MB !!!!!! Unbelievable!!
Maybe the several groups that I was using at the scene was causing it .... when you open a new file, without any hierarchy you lose all groups.