Hi, I hope your morning is going well. I am sorry about the trouble with your grandson. Seeing that he is only 21 months old I do see this as only being a temporary thing. At this age they don't know how to show their emotions so out bursts are not unusual. It may be that he wants more attention or that may be he is trying to tell you something and when you don't understand it upsets him. I would try ignoring the behavior if that helps. By ignoring the behavior it would show him that he won't get anything by using this behavior and also work him on "using his words" to show how he feels. Start with the good emotions by having him say he is happy when he is. It wont be easy at this young age but is always good to start early.
I'm sorry I don't know much about your first question except for the ad's I see for medications that help.
I hope I was able to help and my best wishes to you and your family