21 weeks and losing weight

Caroline
Let me start by saying my prepregnancy weight was 123lbs, I didn't gain or lose any weight in the first trimester, and I'm 21 weeks pregnant now weighing 121 lbs. I do eat when I'm hungry, at least twice a day. I have a very active job, I work at an animal shelter so I'm on my feet all day running around carrying puppies and cleaning kennels. 
I guess all I'm hoping for is some advice to calm my nerves. Thanks in advance.