Hi Sarah, I've tended to find with marathon training that my legs almost always feel tight for the first 2 miles of any run. I think its just the constant overload we put on ourselves. Bit frustrating at times though, as it does make you question sometimes whether you should be out there.
I've become a terrible runner,,, well, i claim to be a runner, but that would suggest I actually run. So I was at home today as I had to go and see the asthma nurse. So I did run there, but I left A bit late to get in 6 miles before (as it was 2 home after), and I totally underestimated quite how hard my first run after my race at the weekend would be, and I was conscious that I needed to get an accurate blood pressure reading, rather than show up just having sprinted there and fob off the high bp with a 'well u did just run here', so, I only managed 3 miles before the Dr Surgery, and it was 2 miles home. A total of 5. If its any consolation, I did seem to loosen up in those last 2. I also have just had a sports massage, and he worked on my lower leg, where I've been getting all those problems. He thinks its caused by a tight gluteus medius, and also tightness in my hip flexors, and interestingly, he said that he doesn't think I should use a foam roller- apparently they haven't been proven to work 
So in summary, my week has been recovery from my half, adn tapering for my 15 mile XC on Saturday, which I may not even be able to get to because snow is forecast again. IF I WANTED SNOW ALL THE TIME I'D LIVE IN THE ARCTIC 