@ozmadman Just to add to what others have said - all stress is cumulative so you could be feeling the effects of other things in your life. Take a note of your overall stress, how well you are sleeping, hydrating and eating.
Here is a podcast (among many) on recovery:
Adding the outdoor rides to the plan could certainly be the culprit. I would suggest tracking everything as we are all different when it comes to our capacities for training and so it is important that you find your own balance.