Hi and welcome to the forum,
Many members arrive here with a similar story to yourself. Not overweight, fit, active, healthy diet. Diabetes is not restricted to those who are thought of as fat, lazy, couch potato sloths as the media loves to make out. It can hit anyone! I would also like a pound for everyone that says they have a healthy diet, but what your healthy diet? Probably not the same diet that is healthy for T2 diabetics that have insulin resistance, metabolic disorders such as raised cholesterol, high blood pressure and a fatty liver, plus an intolerance to carbohydrates. What may be healthy for Joe Bloggs is not necessarily healthy for us, sad though this is.
When you say your readings are averaging now at 8.5, which readings are these? Fasting/before meals/after meals/random? It makes a big difference. Also, which blood tests has your doctor done? Presumably an HbA1c. What was the result of that? (This is the test used to diagnose diabetes, and also to keep check on progress.)
Metformin is a very mild drug, not a miracle cure. It has very little effect on blood sugars apart from the first fasting test in a morning, and even that is a limited benefit. It doesn't work that way. It is a cumulative drug and takes a while to have any effect at all. Diet is the key.
Have a really good read round the forum, and ask as many questions as you like. There will always be someone to help. Meanwhile I will tag
@Daisy 1 for her excellent information post for newly diagnosed.