AUGUSTA — More than two decades after Tracey Stevens-Wheeler had been diagnosed with Type 2 diabetes, the 45-year-old thought her health care providers had made a breakthrough. Over the years, they’ve upped her insulin, and downed it. They’ve given her pills. They’ve recommended a carbohydrate-free diet. Through it all, the Pittston woman has suffered four heart attacks related to her seesawing blood sugar levels, she said, as well as many episodes of dry mouth, disorientation and other symptoms. Finally, about two months ago, providers at a center run by MaineGeneral Health prescribed a new drug, Tresiba, which Stevens-Wheeler injects every morning.