Your pre-natal vitamin should have enough iron to satisfy your iron requirements for now- take it with orange juice or something instead of water, eating or drinking something with vitamin "c" at the same time will help you absorb more iron.
How far along are you? 1st trimester - you should be having (or should have had already) your first pregnancy blood tests.
The results of those tests will show whether you need more iron.
I know with my first, I was drifting off every afternoon-around 2 or 3pm.
I couldn't actually sleep 'cos I was at work, but on the way home or something i'd be keeping myself awake!!
I'd get into my jammies as soon as I got home, sometimes i'd take a little nap around 6 pm.
I'd be in bed, dead to the world by about 9, and up for work again 7.30am.
With my second- I was just as tired, but already having one to look after, I didn't really have the luxury of a nap every day!!
I found getting up and moving around shook off the sleepy most times.