Wow, that sounds a lot like my job... small business, solo IT, heavy emphasis on "other tasks as needed." Some weeks it's felt like I slacked off most of the week waiting for calls to come in (though I've been keeping busy learning, documenting, and updating) while other weeks I'm so busy I barely sit down.

Over time it's been teaching me to say no to projects when they're out of scope or beyond my ability. I used to say "I'll try" to everything which led to some great learning experiences but also a lot of stress and disappointment. Still trying to find some kind of balance there.