You say you were OK while on the Mag Citrate. I have taken magnesium in a better form than that for a quarter of a century, since a neuro put me on it for leg jerks and spasm.
I have only been constipated two times during that period. Once after surgery, and had to be manually evacuated by a nurse. once after a trip and eating bad food and worrying, then I had an intestinal block which needed to be relieved by an oil enema (you can buy oil enemas in the drug store). I use Twinlab Maxnesium oxide, which is one of the least expensive. I take 1000 mg a day.

I also second Sally's suggestion on eating fruit. Yoghurt I'm not sure helps me although I eat it often, so maybe it does. Without fruit and water one is more likely to be constipated.