Bike excercises

On the bike, I don’t get a sore arse as expected. I get a sore back and cramps in my legs. Heres what I’ve learnt on how to stop it.
1. Do stretches in the morning.
2. Don’t go more than about 200k without getting off the bike
3. When not riding (ie, every 200km or so) do more stretches. This doesn’t seem to inspire the strange reactions from other travellers I thought it would.
4. When riding, about every 50km or so, stand up. This helps a little
5. When riding, about every 25km or so, bend the elbows. This heals the elbow stiffness issue i forgot to mention earlier.
6. If require to not stop (gotta make good time), and I still need to stretch, you can stand up, stick you ass out the back of the bike, while  keeping legs straight, put your head/upper body down low (on the tank bag) try to see where you are going and keep control of the bike. This helps a little. Probably best to not do this while trying to pass a truck, considering wind resistance and all that stuff.