Paladins can get -6 or better, depending on items. AC 3 with plate mail, -1 with max Dex, -3 with innate Protection from Evil, -5 with Ring of Protection +2, and -6 for a normal shield.
Your AC is around where it should be. Lizardmen hit hard, so you need to use tactics to deal with them. Web, Entangle, and even Grease are good spells. Every character should have a missile weapon.
Your cleric should have Protection From Evil 10' Radius by now. Use it. You need every advantage you can get.
