Constipated?

He hasn't had a bowel movement since yesterday around 4pm, and he keeps making weird noises and squirming around in his crib... I breast feed, and give him formula, which i'm starting to hear from a lot of people isn't good... but it's what both mine and his doc said to do at the time.. Anyway, What should i do for the time being? If there is anything i can do? I'm worried about him.