URGENT!! Please can someone help with my newborn?? :'(?

Ok so hes 10days old and hasnt poo'd in 3days and hes awfully uncomfortable & when he tries to go to poo he screams hysterically when hes pushin... I dont know what to do ive tried mage, bath, brown sugar & water which the hospital advised then this evening after bringin him to the hospital i gave him prune juice in his formula like i was advised also and still nothing yet... has anyone else been through this or no anything i could do???? Im so upset cause i just dont know what to do to help him.. :(