Well, for one thing, "eating pretty healthy" might not be doing you the good you think it is. Recent research has suggested pretty strongly that when people avoid certain foods when watching their diet, they tend to avoid fats, thinking "fat makes you fat, right?" but what happens is that "lo-fat" diets often contain more carbs to increase their tastiness (because the tasty fats are gone), and it is in fact the carbs that cause the weight around the waist. Try adding a tablespoonful of olive oil every day, it's great for you in lots of ways and it also helps you get the benefit of your fat-soluble vitamins, and delete one source of carbs, especially sweet things. Don't avoid fats, only avoid highly processed meats. See if that helps.
Actually, most of our diets should be carbs. I know high protein diets are a fad, but most people keep confusing people by grouping different carbs together. As antioxidant rich veggies and some fruit and complex carbs such as whole grains and grain-like fruits such as quinoa and buckwheat provide the long lasting energy that is essential especially for a long distance runner. It's the simple carbs such as sugar and white flour that stores quickly as sugar and then fat that are usually meant here, but it's important especially when young people write in that the difference is emphasized. As for fat, well, actually, low fat diets are the ones that have held up the longest over the centuries. While it's important to get the essential fatty acids, especially for athletes, these are most found in foods we don't associate with high fat, such as fish and flax seeds and other seeds even though they do contain the important fats. As for this poster, we don't really know how tall you are or how heavy you are or what age you are. Body shape is often tied to your family heritage in part, though you can alter it by toning. Resistance training does not require weight lifting -- using your own body as the weight, which is what it sounds like you're doing, will work. Resistance bands work. It's also going to be hard to get your body to a good metabolic rate if you keep switching your diet up. If you're going to be running a lot, you're probably going to keep your weight down, but if you eat too little, as it sounds like you are, you won't have the proper nutrition to stay healthy, to have the energy to keep going, or the protein necessary if you want to build muscle -- that isn't really necessary to be healthy but if you want to do that it does take more protein but it sounds like you keep going overboard in one direction and then another. If you can settle on a good, balanced, nutritious diet and just stick with it for awhile your body will do what it's programmed to do. Perhaps you might want to consult a sports nutritionist who can help you understand that once you decide you're going to be doing an intensive training and exercise program you need to eat more, not less, and how to do that. Be wary of fad diets -- you will pay down the road if you skimp on the foods that provide energy and antioxidants. And as for the shin splints, they may in fact be related to your injury -- if you're not completely healed your body will compensate by putting the pressure elsewhere, which is a reason so many athletes keep getting injured.