Constipated infant

Ashleigh
I put a call into my ped but I haven't heard back yet.
 We changed my LOs formula because we ran out of her enfamil and we had some samples of semilac and now she hasn't pooped in 2 days and she poops at LEAST once a day normally. 
I'm definitely getting her back on the enfamil tonight but does anyone know of something I could do to help get things moving ASAP