L.S.
Absolutely it's a very good time to start and if you start now you can continue though the pregnancy. There is a great site called Sparkpeeople.com that helped me a lot to lose 25 lbs while I was TTC (trying to conceive). They have groups of people that you can join for all kinds of different hobby's and things and one of the groups are for people who are trying to lose weight to become pregnant. Then they have a sister sight should you become pregnant called babyfit for mom's who are pregnant to stay in touch and for information about staying healthy through pregnancy. Good Luck!
BTW both sites you can join for free!