What Causes A Cut In The Vagina During Intercourse?

It is 19 years after my 2nd child was born. I am now 44 yrs old, weigh 70kg, average height for a woman, good health (avoid drs). I had an episiotomy and besides a loss of feeling where the wound was and poorer muscle tone in pelvic floor, I also tear superficially along the cut with intercourse (its not that my husband is too super large or something:). Is there any way in which I can be helped?