Everything seizing below the knee

Hey,

Ive been having a problem recently when going for runs. Typically ill do runs between 7-10k. Just this past 2 weeks or so i can hardly make it 2k before my calves and shins completely seize up. I cant figure out why and its driving me nuts! I just joined x-country at my college for the first time this year and ive noticed its really strengthened up my legs, but its the end of the season and they have been fine the whole season up until now... I admit I was in desperate need of new shoes and I just got some. Even still with a few days rest, they are still seizing up after about 6-8min of running. Any ideas?