How long does it take after eating prunes can i poop if i'm constipated?

Depends : Its usually within few hrs but if you have slow motility it may take longer. I would recommend taking a stool softener, be active and drink a lot of fluids. You can also try over the counter miralax (polyethylene glycol). If this is a recurring issue then you need a full history and physical including labs and xrays to find the source.