Ok i need some info...I did a mini quest to eliminate a dragon somewhere near farkarth but i have already kill this dragon and took it's soul and the dragon shout, so when i arrived there was a new dragon there i killed him but it didn't gave me the soul...Is this normal??? i know i have already kill a dragon there but should it give me a new soul???

Once you kill a dragon the respawn will not give a soul so this is normal.

Are the dragons limited in the game because i don't find any i'm level 43 now and i killed many dragons...