Hello Svenks!
What mods do you use? If you use the stock campaign.file, there is a bug that made early escorts to spawn in same place, that made them disappear. So that's one reason for seeing convoys without or with few escorts.
There where some mods fixing this and at the same time reduced single contacts to 20%. You can read about it in this sticky:
http://www.subsim.com/phpBB/viewtopic.php?t=32810
Have you tried Improved convoys? A great mod!
Get it here :
http://www.subsim.com/phpBB/viewtopic.php?t=39445