Loss of Motivation

I've been losing motivation to run lately.  I don't want to but it has happened and I need to find a way to break through it.  I haven't been running nearly enough since I ran the 11 miler.  Between going on dates with my new gal or just making up excuses to do other things, it hasn't been getting done.  I need to find a way to get this motivation back and get my butt back out there.  I'm considering switching things up for a little while.  The switch would involve running less but lifting weights.  I want to build some muscle to help in the weight loss.  I don't mean I will cut out running at all.  I just mean instead of 4-5 milers maybe just doing 2-3 and lifting for 45 mins.  Something has got to change because as happy as I am to have lost 40 lbs I don't want to stop losing anytime soon.