Excel spreadsheets are ideal for this. You can record everything you want (even the number of birds you saw). Take a column or two and stretch them really wide for things like how you felt, etc.
But, I would agree with the above. Record it anywhere that you are comfortable with. Just make sure that you make it so that the information is accessible when you want to look at it.
Also, don't get obsessed with average speed as an indication of progress. It is only good as a very broad measure (over months). Short-term, there are too many other factors (windy, hills, traffic) to make it worthwhile. Distance, what you did (hills, flats, etc.), quality of ride, how you felt, are much better indicators.