What Causes Body Weakness And Drowsiness After Taking Hetrazen And Montair?

Hi I have had persistent cough for more than three weeks now. Doctor suggested some blood tests and my AEC count have come as high as 700. Now I have been prescribed hetrazen 100 thrice a day for 21 days and Montair LC once a day for 21 days again. However I am feeling very drowsy and have weakness in the body as well. What should I do.