Overtraining is relatively simple to check -- take the resting heart rate each morning on waking up. If it becomes elevated above the average, you have likely overtrained.
Weight loss can be had by adjusting portion sizes so they are smaller. Use a calorie counter if needed. The sustainability in weight loss comes from adopting eating habits that also are sustainable. Smaller portion sizes are an ideal starting point... you can eat what you like as you do now, but in smaller amounts. That requires discipline.