Well, when i discovered that i was prgo i had 64 kg, 2 months before i have 57kg ( i stop my training at Gym) . I just lose 6kg. Now i have 63kg and 29 weeks. Dont worry about it. Its normal lose because of nauseas etc.
I try to walk 2 miles about 3 or 4 times a week. And remember that you really do not need a lot of extra calories each day, especially in the first trimester. Eat small amounts more often. That will actually help with any nausea or heartburn you may get.
Exchange your liquid calories for water, that cuts a lot out. And I just walk to pick up my daughter from school like 30 min a day, not fast or anything just walk and I haven't gained weight yet. Or you can youtube pregnancy workouts.