A young woman with a megatits and large sagging breast discovers something strange during an erotic session with her partner

The protagonist, a young woman with a megatits and a large sagging breast, was in the middle of an erotic session with her partner when she noticed something strange. Her nipples were growing larger and more prominent than usual. She dismissed it as nothing until she noticed that her navel piercing had grown larger as well. As she continued to explore her body, she realized that her vagina had also become much wider and more dilated than usual. It was then that she realized that something was very wrong with her body - but what?