I have some pills that are light blue, small and round.. on one side is an "M" in a square, on the other side, the number 15 above a score (line). I looked these up online and couldn't find an exact match to how the 15 side looks.. but I found what I think they are. Says they are Morphine Sulfate SR 15mgs. I am wondering what the "SR" means. Anyone who knows, plz help. Thx