can any mommies help me out ? My little one is about to be 4 months old and is having the hardest…

can any mommies help me out ? My little one is about to be 4 months old and is having the hardest time pooping. She pushes and pushes to go poop , but it doesn't come out. when she finally does poop its a big piece of poop . it ranges from a little pebble to a little bit bigger then a soothie pacifier ( horrible example I know ) . its been like this for a week and I am finally taking her in tomorrow. but do you guys have any suggestions on how I can help her till then ? or any ideas what could be causing it? My first born never had any of these issues so I am not sure what to do. thank you in advance.

sorry for the ubber long post.