It's normal to feel tired, during the first few weeks of my pregnancy I felt sleepy in the day and can hardly concentrate @ work, by 10+ I'll be so tired that I can knock out immediately (i used to sleep @ 1-2am). I dont't think it's caused by the lack of nicotine cos I used to smoke before pregnancy too. About 8/9 weeks onwards this tiredness will go away...dont't worry too much. Just have enough rest, catch a nap if possible.
Enjoy your pregnancy