Joe C is absolutely right! The first step must be consulting your doctor. He or she will help you determine a healthy way to proceed which will be safe for both you and your baby. Make sure you know where you need to keep your heart rate during any exercise and take it on a regular basis whenever you are exercising. From personal experience, I will tell you I was 33 when I was pregnant and was somewhat fit but wanted to exercise if at all possible. Someone recommended Jane Fonda's pregnancy video and I used that till two weeks before delivery. I'm sure you can find it on Ebay or amazon.com or Jane's website. It's simple, not too grueling and helped keep my energy up. I also have read that, more recently, many women are doing yoga during their pregancies but it has to be a class or program specially geared for pregnant women. Walking is always a great thing to do. Stop any exercise if you feel winded, dizzy or exhausted and let your doctor know. I admire your dedication to wanting to be more fit while pregnant but listen to your body and don't push yourself. Sometimes, just keeping up your normal activities is "exercise" enough. Take care--and see what your doctor recommends.
Oh, I also vaguely recall that lying on your back for any length of time while exercising isn't recommended because it compresses some of the blood vessels going into the uterus--or so I think. Please be sure to ask your doctor about that, as well.
