I had a kidney stone removed in dec on left side niw right is feeling dull pain, would they have checked both kidneys then?

Usually: You probably had a kidney stone scan which shows both kidneys, but if your discomfort persists or worsens, i recommend calling your physician.

Yes,...: Nowadays, standard imaging study is ct scan with or without contrast, which will show 3-dimensional projections of both kidneys with highest accuracy than ever, of course, no test yields 100%. At to dull pain newly developing on right side, it's hard to say if it's stone-related or not without detailed history, physicals, and new imaging study since non-moving non-obstructing stone has no symptom.