During the second trimester, your pregnancy becomes more obvious to others. You will become more aware of the changes happening to your body, particularly when these changes make you feel more dependent on others. Support and encouragement from your partner and others will become more important. The changes in your sexual activity often stabilise although they are unlikely to return to pre-pregnancy levels until after childbirth is complete.
During these months you will first feel the movements of the fetus and you will become more focused on its development. You may begin to have vivid dreams about your child.

Physically expect the following changes during the second trimester:

the uterus grows to your navel between 20-22 weeks
you will have colostrum (pre-milk) in your breasts
your nipples may begin to get darker and the areolas will get larger
you may experience changes in the foods your body can digest
pressure on the blood vessels in the lower part of your body increases and may result in discomforts like haemorrhoids or varicose veins
skin changes may occur particularly on the face
Dark splotches may appear on the forehead and cheeks particularly among women of colour. The medical name for this is chloasma. It will fade after the birth, but may not disappear completely.
During this period, the fetus continues to grow and begins to respond to its environment. Here is what is happening:

Fourth month (13-16 weeks)

strong heart beat begins
lanugo or fine body hair develops
At the end of the fourth month, the fetus is about 6 inches long and weighs four ounces.
Fifth month (17-20 weeks)

heartbeat can be heard with a stethoscope
finger and toe nails formed
sucks thumb
responds to noise
grows hair and eyebrows
movements become increasingly vigorous
At the end of the fourth month, the fetus is about ten to twelve inches long (half its length at birth) and weighs eight ounces to one pound.

Sixth month (21-24 weeks)

eyes are open
a creamy substance called vernix covers the skin
skin is wrinkled and the fetus appears very thin
At the end of the sixth month, the fetus is about 11-14 inches long and weighs 1 1/2 pounds. The placenta and umbilical cord are now fully developed and continue to increase in size. Eight gallons of blood a day flows through the placenta by the fourth month. More than a pint of amniotic fluid is usually present by the sixth month.