Female and male housed together, mating too often?

Please help!
I have one couple of corn snakes, (male and female) who have been together all their lives.
They are together in 1 terrarium, and they are mating a lot... Already they mated over 5 times, and the female doesn't seem to like it anymore. She is just laying still and breathing heavily, and her eyes seem a bit deep in the sockets. But still the male wants to mate again. The female is obviously pregnant, her underbelly is swollen with eggs. Is it natural for them to keep on mating? Or should I separate them? Could it hurt her to mate too much? And does anyone know if the heavy breathing of the female is a symptome of pregnancy, or is it something else?
Reactions/help would be very much appriciated!!