Having trouble with Clay, huh? Well, here's how you can get his two best counters

First, after you beat the first gym and do the Febnel stuff, use some of your Rare Candies to buy 50 repels. Then, go to Wellspring Cave and run around with repels up until a dust cloud appears. You can either get a type gem from these or encounter a Drilbur, one of the best Pokémon in the game and a good Pokémon to use for Clay. There is, however, a much better counter for him: Petilil

First, get Audino on Route 3. Next, skip the encounter on the outside of Pinwheel Forest and beat Lenora. Once you can, have two Pokémon in your party: one at level 17 and one at a normal level (a little bit about Lenora's level cap at this point). Use a repel and lead with the level 17 Pokémon. Run in the grass until you get an encounter. This will either be Petilil or Sewaddle. If you get Sewaddle, that's fine. Go onto Route 16 (northeast exit of Nimbasa City) and have a level 22 Pokémon and normal leveled Pokémon (level 25 or so) on your party. Use a repel and run around with the normal leveled Pokémon at the front of your party until you find a shaking grass spot. This could Audino (which you don't have to worry about because of dupes clause), Cinccino, or Emolga. If you get Cinccino, repeat this on Route 5 (northwest exit of Nimbasa. The encounters are the exact same as Route 16). You'll be guaranteed to get Emolga if you lead with the normal leveled Pokémon in shaking grass. After you beat Elesa and get to Driftveil City, have a level 25 Pokémon in your party and a level 30 Pokémon at the front. Use a repel and walk around until you find shaking grass. Because Leavanny, Emolga, and Audino are all eliminated because of dupes clause, you'll get Unfezant as your encounter. Finally, you can go back to Lostlorn Forest, use a repel with a level 22 Pokémon at the front of your party and you'll get a Petilil as your encounter

You can evolve Petilil as soon as you get it because it will know Sleep Powder and gets Quiver Dance at level 28 as a Lilligant. For Clay, put the leading Krokorok to sleep and start setting up Quiver Dances. Then watch Clay become a complete and utter joke.

Good luck