No, NOT YOUR FAULT! Don’t ever think that!
I am the LAST person in the world you would except to have diabetes too. Type2 and thin and 40 years old at dx. I have been vegetarian/vegan for 20 years and ate very healthy, was very active most of the time and I still got it. Believe me, I look back and I keep trying to think what I did wrong (I was sedentary around my dx - did that cause it? I gain a few pounds around my middle but I only weight 130 at dx - did that do it?).
Well, I found out about the genetics of it and my family history (which I didn’t know about before because my mom didn’t tell me because she figured since I was a veg I wouldn’t get any diseases HA!) that my grandmother, aunt and some cousins all had/have diabetes and they found out around age 40 like me. Even my cousin when she found out I had it said “How can you have diabetes? Your a vegetarian.” (well, my cousin is a bit “slow” so I ignore that - I am sure she hasn’t researched her diabetes and figures it was because she was overweight)
In fact, I posted an recent article on here. It is really illuminating and might help you not feel so much like it your fault. It focuses on a bunch of different possible causes - stuff that is out of our control! (ie NOT OUR FAULT). It might help you feel a bit better:
Also, if I missed the post on this I apologize, but why is your doctor not trying you on Metformin?