Shadon, I agree wholeheartedly on intervals, varying the intensity of each ride and making sure you use an efficient cadence.
Your fatigue -- Are you sleeping well? Have your sleep patterns changed? Is your heart rate high in the morning? Increased colds? All of these are signs of over training. I'm sure someone else knows more of the science than I, but these are easy ways to determine if you are over training.
Also, have you changed your diet lately? Too many calories, too few calories, the same for protein, etc. Diet suiteable for restoring glycogen levels? These may contribute to your performance levels. I think one of the biggest struggles I have is taking in the right calories not only during the ride, but after so I get proper recovery. In trying to keep my weight in check, I may eat too little following a big ride and then wake up in the wee hours of the morning just ravenous. This is not overtraining but it sure inhibits recovery because I'm not sleeping.
Frends know gud humors when dey is hear it. ~ Da Crockydiles of ZZE.