There are loads of things you can do. I was really into fitness before I became pregnant and could never sit still so I continued all the way through my pregnancy.
With the approval of my doctor, I continued to do gentle jogs until my second trimester. I rode on a stationary bike, did loads of slow swimming (which always made the life guards nervous
). I did pregnancy yoga and salsa dancing using DVDs.
I did all my exercises in moderation, about 2-3 exercises per week and less as I became bigger and like you, I did a lot of walking.
Apart from jogging, I was able to do all the other exercises right through to my third trimester, just slower and at a more gentle pace.
Most importantly, always listen to your body and have plenty of rest.
Try and do something you enjoy. Happy exercising!