If you beat Whitney with this team, I'd have to say you had a lot better luck than me.
In my opinion, this team is under leveled.
Quilava is your starter Pokemon, so I understand why you train it more than the other Pokemon on your team, it's higher than your other Pokemon by 6-11 levels! If I were you, I'll start training the other Pokemon straight after the Goldenrod gym ('right here, right now,' quoted by Sophocles) (that's just my opinion, you could just train a few and train the others later).
Start with Mareep, because Mareep's Thundershock is the next move other than Tackle (which never effects ghost type Pokemon) with the most PP to take on Gastly's Spite. By then, Mareep should already evolve onto a Flaaffy now, so it you have a lot more power. If Flaaffy fainted in the Ecruteak gym battle I'm sure Quilava can revenge it.
After that, start training up you other Pokemon, you might consider staying in Goldenrod for a while to give Zubat a few haircuts to get it ready to evolve into a Crobat after level 22. If you don't train up now while it's easy, don't even think about having a team that's over leveled in the future. Try to catch some more Pokemon for backups if one of your team members doesn't suit you anymore for some reason, I usually fill my team up along the way to the Elite Four.
Other than that, good luck to become the Champion of Jhoto! Hope I helped!