About to start Metformin. Have a question please

Hi my doctor has today put me on Metformin to help with trying for #3 and because there is a shortage with the extended release she has put me on the immediate release starting with 250mg (1/2 a tablet) once a day for 2 weeks then up to 1 tab (500mg) a day and so on over time. Has anyone been on this sort of dose before?? 
& has anyone had success & with what sort of dose? 
A bit of background on me, I have polycystic ovaries and have 2 children. First one was naturally and second child was conceived on our first round of clomid after trying for a long time naturally. My partner doesn't want to do clomid this time due to the increased risk of multiples so that is why we are giving Metformin a go after having no luck for years naturally. Thanks 😊