Yes, fiddly. So the fizzy drinks are sweetened with different artificial sweeteners. If one gives massive doses of these to a rat, thet get problems. There is one observational study that showed that folk on artificial sweeteners were overweight, but it is more likely that they were overweight, hence the artificial sweeteners, rather than the othe way around. And one should also compare the artificial sweetener to the effect of having real sugary fizz or lots of pure fruit juice.
So, I would mix my artificial sweeteners ie use several different fizzy drinks each day instead of a lot of one; they all state the artificial sweetener on the label.
Well done with the weight loss and feeling better
Best wishes