The problems I had with Metformin in the early days also had a knock on effect with my sense of wellbeing. Especially when it came to an obsession to be close to a bathroom for very obvious reasons. Metformin is a well tried and tested first line prescription for type II diabetics but it can have nasty side effects. The is a slow release (SR) or extended release (XR) version which may make life easier.
Longer term, it's very difficult to know what's changed to cause higher BG now, especially after years of careful diet control. I reached a similar stage after about 4 years of low carb, now my BG is all over the place and HbA1C unacceptably high (55, or was it 59, too high anyway). I personally have found the FreeStyle Libre a godsend because it shows that my high BG happens when I go to sleep at night and not after meals. It also shows the effect of just 2 slices of toast (no longer on my menu plan).
I also found that a self funded c-peptide test and insulin resistance test at least show me, and my GP, exactly where I am. Unfortunately it's unlikely that a GP will ask for these tests, unless he/she is kind.