My 2007 Camry 2.4 4 cyl is suddenly starting to use some oil. Car has 92,000 miles, oil changes at 5000 mile intervals using mostly Castrol GTX 5W20 or Mobil 5000 5W20. At about the 3500 mile mark in the oil change intervals, would need 1/2 quart to top up. At last December's oil change, I decided to use Mobil 1 0W20. Added 1/2 quart at 2000 and again at 4000 mile marks to top up for a total of 1 quart over the course of the 5000 mile interval. I attributed this to it being a thinner oil. I am now 4000 miles into the next oil change using Valvoline 5W20 AC and have had to top up 3 times with a 1/2 quart for a total of 1 1/2 quarts so far. I have checked and cannot find any leaks and there is no oil on the ground. Has anybody else had this happen or know what could be the cause? Thanks in advance.