Very sorry to hear you are suffering this side effect. Metformin is in general, a good medication. There are others in the class such as Avandia. You can talk to your doctor about this. You might try drinking more water, eating more fiber (vegetables, whole grains), taking psyllium seed fiber and walking regularly. Each of those can help. Of course, there is always the laxative option but it's best to try the others first. Take it with meals, this helps. Onglyza is another alternative medication idea. But do please speak to your doctor about any of this. Let us know what you decide.
Perhaps liquid metformin may not make you constipated. Recently. in the past few days it came out in generic. I'd strongly consult my doctor to be on the safe side.