Very tired/sore when bike riding but fine running?

I run everyday so it's safe to say im in shape. I do long distaance and love the 5k. after a race i feel tired maybe dizzy or sore but thats normal for after race. if i go on a run no race i feel great. however if i go for a bike ride within min. i get very tired and i can feel my heart pounding sometimes it gets difficult to breathe and my legs are usually very weak only 3 min in. My quads also feel like they are being squeezed. when i was younger i never had this problem and could ride for miles but over the past 2 years this has started and gotten bad. what causes this?

I can make a few guesses.
1. Running and biking use your leg muscles in different ways. You need to ride more to adjust to the difference. This is the same when going from biking to running and is a well documented problem.
2. You may have the saddle way too low. Your saddle should be set do your legs are close to straight when at the bottom of your pedal stroke.
3. You may be riding in too hard a gear. Gear down so you are in the 80 rpm range or a little more.

Finally, it's likely a combination of 2 or 3 of the above listed things.

Here is some help on the points that MR made:
To adjust the seat;
http://sheldonbrown.com/saddles.html#hei...
On selecting the right gear to pedal efficiently;
http://sheldonbrown.com/gears.html