2 1/2 week old

I was pumping and feeding my daughter that was since she was born, until I stopped producing milk a week ago. So starting Saturday we switched her over to formula and now she is just on formula. She had 2 poops Wednesday but hasn’t pooped since, I can tell she is trying to push to poop but nothing happens and she gets irritated with this happening. She farts but that’s it. What should I do? Is this a normal things? First time mom and don’t know all that much with this situation 😕