There are other things that can be done if you literally can't stomach even Metformin SR. eg going straight onto insulin.
If it's 750 with each meal - from nothing - that's one HELL of a lot to put anyone on, from scratch. They normally start people on lower doses, gradually building up to the full dose, since they are absolutely universally known to cause gastric side effects, but these often subside after a week or two, so they normally add the next dose then, until you are eventually on however much you actually need.
Did you have Gestational Diabetes, or is D just something that's happened out of the blue - AND if you are young enough to have a baby and didn't have GD - are they absolutely 100% certain it IS Type 2?