I flew at 6 and 7 weeks and was fine. Stay hydrated - don't feel bad about crawling over people to go to the bathroom on the flight. My dr said to get up about every 30 min or so just to stretch. I ended up taking a nap for part of one of the flights and was just fine... Good luck!
You're still early so I think you'll be fine..the only is is to make sure you get up and walk around often...this will keep circulation going!
i think the only thing they worry about is if you are nearly due you will go into labour on the plain but if your OB thinks it is ok just take it easy and you should be fine