Considering repeating facelift after 18 months because of loose skin?

Doctor says that facelifts typically last at least 5 years but that my skin has a propensity to sag. (Note: My weight is normal.) I don't have as much loose skin as before the facelift, but the Doctor says there is enough sagging to warrant a second facelift. How common and acceptable is it to perform a second facelift so soon? Is it possible that the results of second facelift will last longer than the first one? I am disappointed that it didn't last longer.Updated on April 10, 2016:I had the first facelift at age 48 in March 2012. It was an SMAS facelift, treating mainly the jowls and cheeks, no platysma. I do not have any medical condition. Doctor said a lot of loose skin was removed, much more than he sees in a typical patient....I repeated the facelift in December 2013 with the same Doctor. The Doctor agreed that facelifts typically last 7-10 years. But he said that my skin has much more skin laxity than the average patient. (I do not have any medical condition to cause laxity)...He said that a lot of loose skin was also removed on the second facelift, about 3/4 as much as the first lift... He also cautioned that it may last only 2 years due to my skin laxity...I consulted a second opinion immediately after second facelift. The second Doctor knows the first Doctor and he indicated that there was no mistake likely made as the Doctor was trained in SMAS lift. And while it is unusual to repeat facelift so soon, it sometimes happens as people age differently.2 years out from the second facelift, the results looks to be holding up slightly better than first facelift, but the jowls/cheeks have still sagged noticeably compared to 1 year post-op.