2 hours was too long for me

I love Walking. Walking is the best exercise for me....I think for many people too.

So 2 days ago, I walked 1 hour and half to get the destination and came back....total almost 3 hours.
I sweat a lot. My whole body was wet!!!!!So change everything and took a shower....then next day...
I caught a cold....felt so tired and coughing crazy. Well....I think this is the sign of "2 hours walking is too much for me", but I was fine and actually enjoyed this exercise.

Anyway, it is really important to know what is the best exercise for you as well as how much is the best for you too.