How much higher (on average) is your heart rate when you wake up? Also, how does it compare to your resting HR at other times of the day. If you are were to be venturing into overtraining territory, it is likely that your resting HR would remain elevated at other times than just upon waking. Try going someplace quiet and relaxing, and laying down for 5-10 minutes, focusing on deep rhythmic breathing - then take your HR. Compare this to what you are experiencing when you wake in the morning.
Also, was the weight change unexpected, or the result of major changes in diet/regimine? Some individuals experience rapid, unexplained weight fluxuations when they are overtrained.
Other signs to watch for are your mood (irritability, lack of enthusiasm, and anxiety/depression are signs of OTS), changes in appetite, rapid fatigue, general fatigue off the bike, and sleep problems. I'd say take a few days off, relax, walk a bit, and see how your HR is doing. If you are experiencing any other symptoms, or even think you are, rest more. 15 hours per week is easily enough to cause OTS if inadequate recovery is occuring.
Let us know how it's going.