Oblivion archer low dps (The Elder Scrolls 4: Oblivion)

I play oblivion as an archer, deluxe edition, at first I liked the game as an archer, but then at level 20+ he began not to dominate at all I kill the average enemy in stealth from 4-5 times from a bow (hardy dexterity 100 speed 100 luck 60 strength 70) who will tell you what to do ? MB I do not understand something in the game for a bow there are nodo arrows with poison to grease or buy special arrows somewhere?