Easter and Passover

I'm used to the concept that Easter happens on a different day each year (unlike Christmas which is reliably on the 25th). But aren't Easter and Passover supposed to happen the same week? I mean, Jesus went to Jerusalem for the Passover, right (the Last Supper)?

So how is it that Easter was last month and Passover is this month? Did someone important miss an ecumenical council meeting?