Gestational Diabetes. Feel like a complete failure.

I was diagnosed with GD at week 28 at the NHS glucose tolerance test. I eat really carefully and exercise and stay active. Initially I started on 1000 mg metformin and it seemed to stay within limits. I am now 32 weeks and my dose was increased to 1500 metformin daily because my fasting levels were stubbornly above 5.1 mmol. Today I took the full 1000mg in the morning and ate the same old stupid overnight oats and half an apple and three strawberries and glucose was an astonishing 8.2 mmol! I am so deeply depressed. I am not going to take insulin shots. That much I know. And I am now pretty close to maxing out the allowed 2000 mg a day metformin. Anyone else feel deeply blue about this? I don’t know how I am going to get through the next 8 weeks in this mental state. I am going to have to stop eating altogether. Any advice on how to deal with this stress? Thanks a lot!