Uncursed carrot juice only gives 3 points, you need to drink a blessed one for the +5. What i usually do, when i have enough carrot juice, i drink blessed ones to get Pe to 20, then hope for a room with smell of carrots.
Don't forget to give Blup some carrot juice for the Swimming skill.
Also, next time you decide to play an Archer, start with Raven starsign and try to get the RCT at lvl 16
(you need some charges of tele and some means to survive under water for about 4-5 turns - just get in and teleport 36, if i am not mistaken, swuares to the left and speak to the Dragon).
Slaying ammo from fletching is your luck, i never got it myself. With Sun's Messenger and a wand of tele and some potions of booze, i'd try some gravedigging. Just teleport away in case of trouble and shoot them with any blessed ammo (unerring would be perfect).
If you get lucky and find Thunderstroke or True Aim, your Dex will train fast enough
.
Have fun and good luck, DE Archers are extremely powerful once you get going. Just avoid some places like Bug Temple and you should be fine.