MayB it's not suitable for your tender skin, have U tried 'ovestin' or 'vagifem'. Or you may not be using enough? Some find that using 'sylc' or 'yes' products as well as VA treatments helps a lot.
How far do you try to insert it, perhaps do it gradually rather than trying to 'push' too far in? Also, are you able to apply some on your finger to make the vaginal walls less 'stiff' B4 you put the dose inside?