Amsta re the aqua or walking - were you quite active before you got preg?
Personally I keep exercising all thru preg (although I am v tired atm so finding it hard) - swimming, yoga etc are great as is walking (as long as you dont get pelvic pain later). I would ask your Dr if you are concerned but you should be ok as long as you take it easier, make sure you dont overheat and watch your heart rate.
Some classes (e.g. preg yoga) want you to wait til 14 wks...
But imo if you can remain a little active you are going to feel a lot better. i always felt better last preg if i went for a swim or a walk or did some activity! you need to be fit for labour after all!!