Tessalon Perles - I have a chronic coughfor a year and a half now, being treated for GERD but not?

... helping me, problen is a lot of clear mucus draining, heard of tessalon, i asked my doctor to prescribe me ant it is helping me a lot, i only cough when i and laying down and mucus accumulate in mt throat my question is can i use tessalon for more than 10 days? or continuously as needed. thanks