So it goes:
First Trimester = tired, exhausted, and tired. Also, nauseous. You're baby bump isn't showing, so no one really understands why you feel the way you do, or how extreme it truly is. You are more bloated than anything, and that gets worse as the day goes on. But, you're happy you're pregnant. :)
Second Trimester = Some energy is back. You forget what it feels like to be nauseous - but you're reminded quickly because you want to eat a little bit of everything. Your baby bump starts to show. You show it off. You buy your first pieces of maternity clothing, and breathe a sigh of relief. You find out the sex, and start buying every blue/pink thing you can find. You forget you were ever tired during this pregnancy.
Third Trimester = refer back to first trimester. Disregard the bump part. Disregard the nauseous part. Just concentrate on the TIRED, EXHAUSTED, AND TIRED part. Baby bump does not allow sleeping. Hips hurt if you lay on for more than 1 hour. Pillow in between legs gets hot and wrinkly. The countdown really begins - because you realize you'll probably sleep better after the baby is born than you are right now.
But, you're still happy to be pregnant. :)
**Note: Multiply all of this x 900 if you already have, say, an adorable but wild 2 year old, to take care of.