your not alone, plenty have gone through this before. the only thing that you really can do is give up running and anything, literally anything, running related up. even if its wearing a pair of running shoes as walk arounds, stop. now when i say "give up" i dont mean forever. just stop running, stop looking at running websits, dont even think about running, stop doing anything that reminds you of running for like a week, 2 weeks, a month if needed.
while your in your "cleansing" process, do whatever your heart desires (excpet run!) and eat whatever you want. of course you can still go to the gym but just dont do anything running related.
after youve gotten ur head cleared and havent thought of even putting on a pair of running shorts then you can start running again.
i know this sounds a bit odd but trust me, it works. i went through the same slump a few months ago and did this, got all my motivation back and felt better than i did before. you just need a brake, thats all. you made running too routineish and it became just another thing you did. getting into a running club or getting a coach or partner too will help you out as well.