Overweight and 5 weeks preg.

So I'm 63 inches tall and 200 lbs. I have been pretty active with working out but my eating habits left much to be desired. I'm basically wondering if it's unreasonable to still be actively dieting through the first trimester. Considering that you don't need and extra calories during your first trimester I would stay at 1200 calories daily including my Prenatals and fish oil. What do you think?