Suggest Medication For Constipation

my baby is 5 weeks old. he has these spells where he acts like he needs to have a bowel movement - he stiffens up, works really hard, grunts, gets red in the face, and sometimes ends up crying. but most of the time nothing happens - he doesn t even have a bowel movement (when he does actually have a bowel movement, he doesn t even have to work like that... it just comes). he s obviously in some sort of discomfort when it happens, and those spells are quite frequent. what could it be?