Losing weight during pregnancy

I was just at my ob yesterday and she didn't seem too concerned bcuz the baby's heart rate was 154, but I am worried about it. In the beginning of my pregnancy I gained 4 pounds (up until 9 weeks), at my 12 week appointment I had lost 4 pounds, yesterday at my 16 week appointment I had only gained 1 pound.

Don't get me wrong, I have changed a lot of what I did during this pregnancy so far. I went from drinking sodas (Fanta & Sprite) daily to drinking a soda once a week and started drinking more water, I have also been more physically active these past 8 weeks. And Monday (July 4th) I went to a freedom festival to watch fireworks and let my daughter enjoy the festivities. The temperature that day (including the heat index) was 105°F so I drank more water than I did anything so I didn't dehydrate. Then add in all the walking (4 hours worth) that probably contributed to why the scale said I only gained 1 pound...should I be worried???