You could triple your bra size -- and then some
Breasts usually become swollen and enlarged in the first trimester because of increased levels of the hormones estrogen and progesterone. That growth in the first trimester isn't necessarily the end, either -- your breasts can continue to grow throughout your pregnancy! And they won't just grow; they'll be tender and sore, too. Even the areola, the area around the nipples, becomes darker. (But don't worry, with the exception of the darkening of the areola, which is permanent, these skin changes will likely disappear after you give birth.)
You could look in the mirror and see a pimply-faced teenager
You may have heard about that "pregnant glow," but you might be one of the many less fortunate moms-to-be who are blessed with acne instead. When you're pregnant, the skin's sebaceous glands increase their oil production, making your skin break out in pimples that could be reminiscent of when you were going through puberty.
You could become a raging lunatic
Your hormones are going to be out of whack. Your moods will swing. You'll start to feel a loss of control because being pregnant is the one thing you can't control. You can cry at the drop of the hat and bite someone's head off for no reason at all. You might also start to worry about, well, everything. Don't worry, it's all normal. Now you just need to convince your husband of that!
You could sleep a lot (even at work)
If you thought you weren't going to get tired until closer to the end of your pregnancy, think again. You could be exhausted from the moment you find out you're expecting (or even before). Your body is working hard to support a growing fetus, which can wear you out. You might find the need to take naps (even when at work). Do your best to manage your exhaustion during the day by making sure you're getting enough sleep at night and enough iron. (Too little can lead to anemia, which can cause excess fatigue.)
You could smell things, really bad things
Often, one of the first signs you could be pregnant is that you have a heightened sense of smell. Brace yourself. Having super smelling skills will only add to the nausea you could already be experiencing and send you running for the toilet. Why does this happen? Those darn hormones strike again! And don't be surprised if you open the refrigerator and inhale a pungent odor, but no one else in your house can smell it, only leading you to feel crazier than you already do! Ah, the joys of pregnancy.