You can use “all these (weeks/months/years)” to talk about something that has been happening for a long time-- or feels like it’s been happening for a long time. The phrase also implies that the listener knows something about these weeks, months, etc, or experienced them together with the speaker. There is a shared, “insider” feeling that “many years,” for example, doesn’t have. 

I’ve been waiting all these weeks to hear back from them.

All these years I thought she didn’t like me.

You can also say “all this time” if you don’t want to specify the number of weeks, months, etc.

All this time, I’ve been saying it completely wrong.