Have you tried using a lubricant? This may help. Some women will use special products to stretch the perineum prior to childbirth. Perhaps this is something you could try. Unfortunately I can not remember what the products are but if you google search it you may find it. You could post a querie in the pregnancy forum here and see if anyone has any experience with them. All the best.

I find creams made of beeswax to be very helpful for dry, damaged or cracked skin. We're talking about the skin between the opening of the vagina and the anus, correct?