Your priority at present moment should be your health and a baby.
You wrote that your weight is 170lbs but what about the height?Maybe you are within a healthy weight range and do not need any dieting and this is only in your head...
Whatever the case,all you need is a good nutrition plan which includes all of the necessary nutrients for both of you, a reasonable energy intake and a psychological support will work miracles too!
Exercise during pregnancy will not do harm-20 minutes or more of brisk walking every day will be great!That will elevate your mood,you will get fresh air and in addition burn off a bit of calories(of which you should start thinking less at this point).
Gd luck!