You may need more iron, but I also recall having alot of fatigue during that time period. Since you have 2 other children and are working, in my mind, it's TOTALLY normal that you are this tired. Your body needs the sleep to start building that baby. I remember coming home from work with my two year old and just laying on the couch for an hour before I could fix dinner, going to bed at 8:30 am sleeping 8+ hours and then having that same fatigue at work. One thing that might help is to limit your carbs during the day as those are very sleep inducing. I found that if I had protein in the morning (eggs) and just one slice of toast and then a salad with meat/fish (salmon is very low in mercury) or leftovers from dinner (meat/veggies), I did much better in the afternoon. Also, if you've dropped caffeine for this pregnancy (a good thing for your baby), your body may still be in withdrawal.
However, if it doesn't resolve by around 12-16 week timeframe, I would ask your doctor to test your Ferritin (the most accurate test for iron deficiency) AND to test your thyroid. It is not at all unusual for hypothryoidsim to be triggered during pregnancy. You may have been borderline before and pregnancy pushed you into the hypo range where you might benefit from thyroid hormone. This is REALLY important for the develpment of your baby, as well, I strongly recommend you talk to your doctor about this, particularly if the fatigue persists.