Losing Weight While Pregnant

​I heard that it's not an 'okay' thing to do, but I've also heard that it's okay to lose weight in your first trimester (I'm 5wks), as long as you gain in your second trimester and so on.

​I was in the midst of losing weight, took a little break for a couple of weeks and that's when I happend to conceive! I don't see my doctor for 3 more weeks, I just wanted some opinions if it is okay to lose some weight and get fit or more fit during the very early weeks of pregnancy. Nothing strenuous or too rigid. I usually walk or power-walk, and sit ups to tone my stomach along with a few other workouts. I really wanted to tone up some more in my stomach area and my arms especially. I'm not exactly "chubby", but I'm not very thin or all toned up. Is it okay as long as I'm eating healthy? What about fat loss? I'm pretty curious.