u really shouldn't try to lose weight while pregnant. but if u get bad morning sickness u may not have a choice. try to keep ur weight the same or if it bugs u talk to ur doc. good luck dear!
You never want to intentionally lose weight, but women might in the first trimester due to nausea/vomiting. Depending on how sick you are you could lose 10-20 pounds. I myself lost 25 pounds while pregnant with my daughter. Just try to make sure you're keeping yourself hydrated.