I recently got my lvl 5 eevee from the eevee quest but all my other pokemon are in their mid 40s. Does anyone know a good spot to hunt or good way to level up my eevee faster? It's taking forever!

well i would suggest u to finish upto 8th gym first n then lvl on victory road..after that u can unlock cerulian cave by finishing johto too and doing the quest.You can use membership medalion/exp boost if u are able to buy.If not do struggle up to 8th gym Enjoy

There aren't too many options to level up your Eevee quickly during the story. However, if you have a false swiper Pokemon, you can swipe a wild Pokemon (preferably as highest level as possible) to 1HP, keep spamming false swipe until your swiper dies, swap into your Eevee and use quick attack to secure full EXP. It should bring her up from Lv5 to somewhere in the 20s or 30s depending on if you have a membership.

Like he said^^ mt silver best for kanto after all gyms

You could just buy a cheap lvl 100 poke for like 50k fly thru Kanto until you hit dragons den in the next region which is 2nd fastest leveling area