What type of beer are your brewing? What temperature are you fermenting at? Seems odd that you're still seeing active fermentation for that long. For most ales, the 1-2-3 rule works (1 week in primary, 2 weeks in secondary and 3 weeks in bottle). Is this a lager?
I don't follow that rule at all, and wouldn't suggest anyone keep their yeast on a schedule like that. They work on their own time depending on the environment we give them to work in.
First primary of only one week sometimes will not get you to terminal gravity. I don't even check its gravity until the end of week two. And most times it is done then, some times its not.
Secondary in my opinion has no benefits unless you are 1) lagering, in which you want to get it off the yeast cake 2) adding some kind of flavoring i.e. cocoa nibs, fruit, etc. 3) going to bulk age for a period of time longer than 2 months. On most my ales I leave in primary for another week after the initial 2.
Three weeks in bottles is a good period of time, but I've had some perfectly carbed after only one week where others won't taste good for another month or two. But it is important to make sure you are at a stable gravity before bottling, so I check gravity again at the end of week three. If its the same I bottle, if its not I wait three more days and check again.
I like the simplicity of your 1-2-3 rule and once you get a recipe and fermenting profile down pat you may be able to find a yeast strain that works with all those variables and reculture it for future brews to make sure it behaves the same. But I never trust only time duration.
For the OP, seeing bubbles after fermentation has completed is perfectly normal. CO2 has disolved into solution and slowly degasses. You have to take a sample and test its gravity, then wait three days and test again. If it's the same, bottle on and enjoy!
