Welcome to the forum, Gale.
None of us on the forum are able to offer medical advice, so the best person to speak with is whoever prescribed your metformin slow release (Metabet SR).
However, it is useful for you and prescriber to consider a few points eg Did you take regular (not slow release) metformin before slow release version? How long have you been taking Metabet SR? Sometimes it takes a few weeks or months for your body to get used to a new medication. Plus, you need to monitor your physical activity levels and diet to get the best from yor medication - that really means self checking blood glucose levels with finger prick tests and a meter. I hope that your GP is willing to prescribe some strips, but if not, sometimes buying a pack of strips and showing GP the results, and more importantly, how you make use of the results to improve your control.