This is our first go-round with chickens, and we are having so much fun. Our 3 week old RIR female chick is having a hard time pooping. She is otherwise content, eating, drinking, playing with our other chicks, but for some reason when she needs to poop she has difficulty - fluffs out her feathers, sometimes closes her eyes, makes a strange chirping sound. None of the other chicks are bothering her when this happens, and after a minute or so she is able to go. I've observed her pooping without struggle in the last few days also, but this seems to be a trend. They were all vaccinated for Mareks, and are on medicated chick starter. We have added grit to their starter since day 3. We've taken them outside to let them scratch around for a bit in the last week, and we also gave them some dried mealy worm treats last week. I've added electrolytes and probiotics back to their water since I've noticed her struggling. Any tips? Do we need to be concerned?