1. Yes you can still have sex (my OB informed me), just do not try something too fancy------
2. if you are only 3-4 weeks, you can still exercise, bottomline is: you do not want to exercise too hard and you can breath easily; your heartbeat should not be exceeding certain level (cannot remember the details sorry)-------I did my martial arts training for the first two months (without knowing I am pregnant), every time 1-2 hours very hard workout. I did not have problem
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3. Again for exercise, it depends on what you did prior to pregancy, if you used to be very active, you can still do what you normally do, just do not make yourself too tired. Exercise during preganancy is really good. I hiked, mountain climbing, etc. till I was almost 6 months, then I do 1 hours walkings every day. Make sure you remain hydrated.
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Safe way is to review it with you OBGYN. based upon your situation.---
4. carrying heavy stuff, might not be good.
BLESS