Had the same problem the first night I slept at 16,000. Took diamox the next morning, rested for a couple of hours. Did a carry to 19k the same day, moved to 19k the next day. Never had any problems after the first night, even though I forgot to talk diamox on the day moving to 19k. Since I didn't have any problems, I didn't take it again (doc said not to stop taking it after starting, but since I already did and was still alive, I just went with it.)
My wife and I have both slept over 19,000' for up to six nights in a row. The only difficulty we've had was my wife complained about being overly tired the first night at 16,000'. The second night she took 1/2 a Diamox just before going to sleep and that appeared to sort everying out. She didn't take any Diamox after that.