Bottom bracket bearing issues
Take everything apart,get all the grease out of the bb and feel inside where the bearings go,it should be fairly smooth,do this to both sides and compare the "feel" of each..If it doesn't feel right(burrs,cracks) there's your problem...I just replaced the bearings in my bike and they were 1/4 inch but your bearings will probally be metric in that general size,it's easy enough to find online...don't skimp on the bearings,get grade 25 bearings,there the best...amazon has them for short money and good luck