I run XC and Track for the University of Wisconsin.....So maybe I can help you out a bit
Doesn't really sound like it's diet related. Eating healthy is fine and all, but it doesn't really make or break you like that.
Sounds like you haven't been running in a while. It's not such a great idea to just jump in and flog your body like that, but what's done is done now. It's most likely muscular, but if not, theres some tendons that run from your ankle up the inside of the calf. Can you feel if it's muscular or not, or can you not tell the difference?
If it's muscular (most likely is), you should be:
heating it up before you run and stretching it LIGHTLY
stretching it lightly after you run, followed by immediately Ice cupping it (fill up a dixie cup with water, and freeze it, and peel back a bit of the top of the frozen cup and massage that directly on the calf. This is a bunch better than using an ice bag.)
If you are just building up mileage, try running a mile a day for 3 days, two miles a day for the next 3 days, take the 7th off, three miles a day for the next 3 days, I'm sure you get the point.....Just increase mileage slowly untill you get to where you want to be.
Hope it feels better
And remember, it's not a cramp, it's overuse of a muscle that's not used to it (most likely). overstretching it could hurt it.