were are all these dragons coming from, Alduin has been dead for three months so whats bringing all these dragons back to life. is there anther dragon out there who can rise the dead???

And why can't I use the rise the dead shout , i was there when Alduin used the shout so I know the words
I heard him say them. If I can learn DRAGONEND by hearing the words why can't I learn this.

Firstly, because the plot says so, secondly, the words alone are not enough, you need understanding, which only comes from the dragon or event imparting the understanding. So you may hear the words, but only Alduin understands the words and has the knowledge. Even if you kill him, you can't learn the knowledge since you can't absorb his soul.

Who says Alduin only raised Dragons around Skyrim? He could have raised them up in other parts of Tamriel. They just come to Skyrim because they want to hunt the dragonborn and try to kill him/her.