What Happens to Your Body in POF

The Initial Cause
In POF a genetic, autoimmune, environmental, or toxic cause triggers early rapid destruction of the primordial follicles (these are the "pre-follicles," basically just eggs in their storage form; for more review go to the "Understanding the Female Reproductive Cycle" section of the site). 
The Hormone Response
Because the follicles are destroyed, the brain keeps sending FSH out to try to work harder and stimulate the follicles. This is why FSH levels are extremely high in POF; your body is trying REALLY hard to get some follicles to grow, and receiving no feedback. Because the follicles aren't there (and these normally secrete estrogen), your body's estrogen level drops way below normal. 
Consequences of the Hormone Response
Part of the temperature-regulating part of your brain (the hypothalamus) changes in response to the drop in estrogen levels. The "thermoneutral zone" in the hypothalamus narrows and the body becomes much more sensitive to subtle changes in temperature. The brain then sends messages out to your blood vessels and they dilate, causing the feeling of heat at the skin. Hot flashes can occur during the day or at night. 
Low estrogen levels affect the vagina: the skin gets thinner, drier, and less elastic. The skin may tear more easily, and it may be more difficult to lubricate naturally during sexual arousal. Low estrogen levels also affect the bones: the bones begin to break down faster than they can rebuild (normally there is an equilibrium of building and breaking down). This leads to osteopenia (pre-osteoporosis) or osteoporosis.