If you're going to use indoor trainer "speed" as a progress metric, it will be more reliable if you make sure that the rear tire is pumped to the same pressure and the drum is cranked down to the same resistance every time. And keep in mind that your indoor speed may not correlate to outdoor real world speed. That is, don't be discouraged if you can do 24 simulated mph on the trainer but only 20 real world mph outside.

Also, are you using a heart rate monitor?