iphone connects disconnects

Hi, have an iphone 6 64 GB. When I connect it to my Macbook Air, it begins connecting and disconnecting really quickly (more than once every second) and I can't transfer anything to itunes of backup my device. Very annoying. Am using the original USB cable, and have tried both USB ports. Same result.

Does not happen on my windows PC at office (very sad!!!)

Iphone 6 - 64 GB / Macbook Air Yosemite