Can you fly with low platelets 5k?

Be seen. That is low enough for you to spontaneously start bleeding. You should be seen immediately by a hematologist for a diagnosis and treatment.
Type? That's a pretty low platelet count, you would want to check with your doctor prior to flying, one risk would be the lack of ready availability of medical care. Another would be possible effects of turbulence causing some trauma. Usually flying is pretty safe though compared to the alternatives. Short haul safer than long haul. Best to get platelet count higher first. See: http://goo.Gl/mco9s.