I was doing aerobics and sit-ups until 8w pg, as well as walking and stuff, so I don't think it will affect you too badly.

If you're on a strict diet, your body assumes you're undergoing a period of starvation so can't support a baby, so you won't ovulate or get AF because your body thinks you can't nourish yourself and a child - the more crash diets early on, the lower your fertility in later years.

Yoga can help with TTC - I have some TTC Yoga exercises to make you more fertile in the Yoga book I have.