Having to add oil between oil changes

You might still be burning it, just not seeing the typical blue smoke. Try a leak down test, and see if there is excessive blow by. You can also check the PCV, a clogged PCV can cause oil blow back, they are easy enough to clean or replace. Other things like worn valve seals are not really DIY jobs unless you have the skills and tools, you'll need a shop for that one.

Welcome to the club! Some of the I6 engines do this, some don't with no sign of oil anywhere including the plugs. Some of us have problems with eating up synthetic. If you're using synthetic, try swapping to a blend or conventional. The I6 does not have a PCV valve, but does have 2 PCV hoses. Check the one under the plastic resonator, and the one right by the PCM. Another place to check are your sparkplugs, if there's oil in the sparkplug wells, then you need a new valve cover gasket. If nothing is found, like mine, just live with it, and keep oil in it.