Am I too small?

These pictures were taking from the last two weeks. I am currently 23 weeks pregnant. I've only gained 4-5 pounds , I was 139 going into pregnancy and about 144 now. I feel sometimes my belly looks bigger than other, lately I've been doing some toning excersises for my tummy and lower back, but nothing intense or over 15 minutes. I kind of feel like I look smaller the last few days than this other picture from two weeks ago.