health questions!

Cramp is normally caused by salt deficiency. Sport rehydrate drinks help. A drink with plain salt should bring near immediate relief.

also dehydration. I used to get cramps when i never drank water, just coffee. Now that i drink water as well, i never get cramps.

Salt has helped me too. I was riding in the hot weather in Singapore, drinking enough water, but got cramps afterwards anyway.

As I don't like the taste of sportsdrinks, especially when really exhausted, I get nausea from sportsdrinks, so I take salt tablets before leaving.

A good idea is also to keep moving a little afterwards. Just lying on the sofa after an exhausting ride promotes cramps.

Eat bananas if possible to help with potassium intake, keep a good balance of salt in your diet and drink plenty of water. As above Ibuprofin can help in moderation - just don't use it as a habit.
I'm not sure what your riding habits are, but a cool down period is a good idea. Ride more slowly as you appraoch your final destination.

and sounds obvious but make sure your seat is adjusted to the right height so that while pedalling, your legs aren't constantly bent. at the bottom of a revolution your leg should be properly outstretched.