why has my photostream stopped working

I have just notcied that photstreaming is not working.

I have iPhone, iPad and iMac.

Pictures taken on the iphone are not being sent to my other devices. This was working up until last week.

I have checked iCloud settings on iPhone, Picture settings on phone, settings in iPhoto on iMac. They all have photstream turned on.

At home I am also on WiFi and still does not matter. Took a shot over wifi at home and it was not replicated to other devices.

Photos are not syncing across devices.

I would appreciate your assistance on this please. Especially since it was working for me last week and now it has stopped all of a sudden.

Thanks and I look forward to your reply.

...Bruce