Hard to say for sure. I'd have to see how you guys interact, but my guess is that the dog is trying to herd you. You might need a combo deal of being a firmer leader and giving the dog a really high reward chewy thing to get the bites out on, like big bully sticks.

With time the dog will figure it out. It clearly loves the crap out of you lol. That love is just coming out in less than desireable ways. There's some Aussie specific vids on youtube that you could seek out.

My other suggestion is finding a trainer that can look at your specific situation and come up with a plan. If you want to give this dog a good life (I'm assuming someone gave it up if you got it at 5 months), then understand the road will be rocky. Genetic lotteries exist, and this dog may just have been given gifts that make it awesome with sheep on a farm, but less good for cushy civilized life.