Make sure you don't have a blockage somewhere. My diy started letting off very few bubbles, except when I would shake it. Turned out, one of my check valves was blocked.
You shouldn't have to shake it to get bubbles out. In fact, you really don't want to shake it. The dissolved co2 reaches an equilibrium with the surrounding environment, when you release that dissolved co2, it has to build up again before the pressure builds. On top of the time it takes to build up, you've also wasted that co2 that exploded out.
I think where you read to shake it, it mean to lighting shake(not even a shake, just turn it upside down once or twice) to mix the yeast with the sugar.
EDIT: Don't shake it and espeically don't shake it really hard. Yeast don't like the violence. After initially mixing the contents, you don't ever need to shake the bottle. Just let the pressure build on it's own. Sometimes, to get good output, my bottles can take up to 24 hours. They'll start bubbling after just a few hours, but to get my normal constant output, it'll take 24 hours(again, for me). This will then last close to two weeks.