What does it mean when a dog keeps yawning, (apart from being tired), my dog yawns everytime you stroke him or tickle him, its almost like a sign hes content and happy.

Sometimes a yawn can mean indifference or even a slight defiance.  Didnt mean to burst your bubble lol, ;)

It can mean contentment as well Sandie :)

It can also be sign of stress!

Thats the word I was looking for JG :)

It can also be a calming signal... Apparently if you look away and yawn this tells the dog your not worried...lol so now u need to pick which it is at different times :D

As he only does it when he's being stroked and tickled under his ears I think I will put it down to him being happy, I know he is not stressed and he is oviously happy and enjoys it because he pokes my hand to continue if I stop.

I would say he was pretty content then ;)