@Vic01 - There are so many reasons why you could be seeing these impacts after all this time. Sometimes, our bodies just change a bit, and having had a baby recently (in terms of the ful amount of timeyou have been using Metformin), it could even be your renormalising hormones getting into the mix.
One thing I'd definitely ask, we I in your shoes, would be to check what brand of metformin was being dispensed to me. As with most other meds, I feel fairly sure your Metformin tablets will have other ingrediaents in their formulation, as well as the metformin itself.
As an example, the only medication I take is Levothyroxine. I can take any brand the pharmacy likes to dispense to me, except Teva. If I am dispensed Teva, I a nauseous all day, every day until I move onto another brand. My prescription is now worded to state Teva should not be dispensed.
I have no idea what the ingredient is that makes it this way for me. It's likely to be a filler or something.
In the meantime, could you maybe try taking your Metformin at lunch and dinner (or whichever meals you eat), rather than on an empty stomach? Metformin works on a therapeutic dose basis, so varying the timing a bit should make a discernible difference to its workings of your body.
Otherwise, if your GP won't prescribe the extended release variant, try asking the pharmacist for another brand, and see what happens? It could take several days to change though.