I've been running since my early teens so I can't say I know exactly what you are going through, but I do find myself lacking motivation a lot!  One thing I recently did was set a mileage goal for the month and then I created a spreadsheet to track myself.  It worked well and I met my goal but this can be very dangerous for a newer runner and can lead to injuries.  I have a friend who started running after 40 and his problem is overuse injuries and is still getting over a stress fracture.  

But now on to my advice.  Slow down!!  Finding your pace is on of the hardest things to do, imo, but I often see new runners trying to go way too fast.  Your endurance will improve when you're not running to the point of being out of breath.