You have to remember too, different brands of clothes can be off in sizes. I have noticed this lately with pants too. I hate jeans lol. I bought a pair of dress slacks from Walmart in my normal size. But I went to Kmart the same week and the size I bought at walmart didn't fit at Kmart! So don;t be discouraged. It could just be that Old Navy makes them a little smaller than another brand.
Have you increased your activity level? Even walking for 30 minutes everydayor every other day will make a difference. My doctor has order me to get a thyroid test. I have changed my eating since December. I lost 15 pounds and I am stuck there. I am always on the move everyday and she said she can tell because my legs are pretty muscular except for a pocket of fat on the inside of my up thighs whick I can work on by taking stairs instead of elevators. But she wants me to get the thyroid test. She said if I do have a thyroid problem and I get on the medicine, she said if I keep eating habits the way I have been and increase exercise somehow, I will lose 20 pounds easily in the first month or 2. Now my problem is finding the time to go get the blood drawn. Maybe talk to your doctor about this as well. Good luck and keep in touch!