It could be a lot of things, but mostly, and pretty much what everyone before has said is training.
So first and foremost I don't know 100% what you mean by an empty stomach. I hope you ate at least hour and a half to two hours before running? Your body does need fuel to get you going. I usually eat an hour/hour and a half before hand. Foods high in potassium are a good bet. Potassium and magnesium will help with cramping. That doesn't necessarily mean if you eat a single banana for the first time an hour before you run it will directly help, more so those kinda foods (dark leafy greens, beets etc) should be added to your diet regularly. I know those aren't fun foods, but add them to your smoothie and its an easy, fast way to get the nutrients you need to fuel your body. When you run your using more resources then ever before.
Also, water, water, water! Dehydration can be a major cause of cramping! And as a runner you need to consume even more water then before. There are a lot of great apps for your phone that will not only tell you how much water to drink (calcs your weight, height, weather conditions, exercise output etc) and it will also have the option to remind you to drink water! (Water Your Body app). Also you can add a 'pinch!' of salt to your water to help provide electrolytes and help absorb the water (you shouldn't be able to taste the salt though, that's too much!). But also there are great electrolyte drink recipes on the internet that are way better then Gatorade!
I'm also kinda new to running (been a year since PHM got me into it) and I now coach Field Hockey and a good go-to trick for cramping while your running is breathing in through your nose and breathing out through your mouth! It was a tip from a Navy Seal! Just slow your pace down a bit try that breathing trick and its starts working in a minute! Works for me and my girls (who just whined about doing a long jog and resorted to that breathing style).
But also like everyone said above, try a good couch to 5k training program. Or just slowly increase each day as long as your body allows! You'll get there! 5k ftw!!!
