What Causes Insomnia After Taking Cheratussin AC?

Thank you for listening to my questions. Recently I have started taking Cheratussin AC Strup and have been taking 2TBS four times a day for two days. I think it is odd though that when I take the medicine I have insomnia and jittery energy, like I have had coffee. Also I have been coughing more. The coughing is less severe and I am feeling no pain but I was wondering ifthis was normal. Thankyou.