For me the horrible aching joints kicked in at about four to five weeks after starting on Letrozole. They kept me awake at night - had to get up to take Neurofen - but they eased off after two or three weeks. I have also had the headaches together with feeling a bit sick. The bad headaches eased off but I still get a slight headache every few days. The aching joints made me feel like I was about 100 and my 92 year old mother in law seemed positively sprightly compared to me, but it certainly got a lot better in quite a short time and now I am fine with just the occasional twinge. Only advice I can give is keep on with the painkillers and rest if you need to. If things don't improve get to your GP for stronger painkillers - I think some people have Amitriptyline which is an antidepressant but is also used as a painkiller at a different dose. My bone scan showed I have slightlythinning bones so I am going to have to start on calcium supplements and Vitamin D. Also my cholesterol is raised and if it doesn't improve on a low fat diet I will have to take a statin, so will soon be rattling at this rate. I hope things get better for you soon.