If you're considered high risk then follow the doctors orders. Also, she probably doesn't want you to risk a miscarriage due to your busy schedule and strenuous activities. Proceed in moderation but you certainly don't have to stop, especially if running has been a part of your lifestyle. Travellin by plane is fairly safe thru 32 weeks, then car thereafter. Just make sure to move and stretch to avoid numbness and clotting. Good luck!
Only your doctor knows why she wants you to slow down, so it'd be a good idea to ask her. My OB told me that too...she actually told me no exercise for a few weeks, and to slow down at work as much as possible. She just wanted me to be cautious until I got out of the first trimester, when the chance of miscarriage is high. I always figure that when the baby's here my whole life is going to change, so I might as well get used to putting her interests first now.