I have recently noticed that it has stopped working after 6 hours instead of the usual 8-9.after about 9 hours i get mild achy and fluish symptoms.should I ask for a higher dose or switch to other drug?any suggestions of which one?I have chronic lower back and knee problems and do not abuse the meds.I take the oxy every 12 hrs and have the endone for breakthrough and for in between doses.please advise as it would help me alot in how to discuss this with my g.p