You are in the strange position of being in a sort of limbo. But for your brothers condition, you would have been diagnosed as type 2. And later on as the honeymoon period petered out, and your sugar levels really went haywire, further investigation would have shown LADA.
Whilst your Pancreas is still producing sufficient Insulin, treatment is much more tricky, but i'll leave that to our LADA members, who have far more knowledge than i do.
3.9 is actually a normal level, that many many people can see and much lower, until their liver kicks out some Glucose to normalise things.
The 13.9 could have been due to what was eaten, if you could give an idea of the sort of meals you have, it may show ways of improving things in the short term.
As far as i'm aware you basically need to live as though you were type 2, until the Pancreas insufficiency reaches the point where Insulin will become necessary. But again our LADA bretheren will know more than me.