That is normal even with no XP boost items. At least unless you set XP below default or don't kill a lot of zombies. Of course, I also don't sit around doing nothing during the week, so I raise my game stage a lot just through normal activity... usually killing zombies everywhere. If I don't get at least 3 levels on horde night, something is wrong. Sometimes it is lower in later levels before the XP to level stops increasing, but not in the early or late game.
I also get ferals regularly by the end of week 1. They aren't that difficult to deal with, at least with a spear. I'll even attack them on day 1 if I see them wandering around town. Armor doesn't even really matter all that much in this game. Sure, if you perk into it and have Q6 armor, you can last longer than without, but I never perk into it and I'll do T6 quests with Q3-4 armor without a problem. Weapons and weapon perks are far more important to survival.
Anyhow, that doesn't mean the XP boost shouldn't get lowered. Maybe to 50%. I don't really care because nothing they do to the sledgehammer will ever get me to use it. I hate slow weapons.