I have a level 5 base; should I be able to be attacked?

One downside to the game is that any base can be attacked no matter the level. Although initially your will have a shield this will run out in a short time. It is rare for low levels to be attacked though as attacking bases such as 5 will not gain the attacker much. There are shield items that you can buy for diamonds of get as rewards which will protect you from attacks temporarily. Finding an alliance that is not currently at war will help too.

War protection is to do with the doomsday events and is an alliance war period when other states alliances can't declare war. but that is not a protection for your base.