Limewave,
I think you are just going to have to give it more time.......... probably not what you want to hear, but a fact. Major surgery takes a lot out of a person, 3 months just isn't that long.
Maybe set yourself easy goals, ones you are pretty sure you can reach now, but might stretch you just a little bit. If you want to turn around at 5 miles, do it. Say "Today I will ride out 5 miles and then go home. That'll make 10 miles. That's pretty good!" Do it a couple times in a week, and the next week, add just a mile or two. If you are still tired, hang at that mileage till it starts to feel better. In between ride days, go for walks. Walking is wonderful for recovery.
Spin classes can be great, but don't overdo it. They can also be pretty intense if you try and keep up to everyone else. Use your resistance knob on the spin bike to keep it at a level you are comfortable with until that starts to feel easier and then move it up a notch. Every time you are able to go a little farther or up that resistance just a little bit, be proud of yourself! It doesn't have to be large improvements all at once. Small improvements will add up. Give yourself this fall and winter to gradually work your way back into shape and you can look forward to starting out the new season in 2004 refreshed and ready go go. Good luck!
Time is a companion that goes with us on a journey. It reminds us to cherish each moment, because it will never come again. What we leave behind is not as important as how we have lived." Captain Jean Luc Picard