Been noticing less power each day, had a p0420 for about a week. Loss of oil and coolant over time with no leaks out the bottom. Any suggestions?

 

If you're not seeing anything on the ground, and it's not filling the crankcase, I would have to venture potential head gasket, or more likely the turbo.

If you say it seems like it's been losing more power daily, easiest check would be pull the intake off the turbo. Just reach inside and see if the wheel has play side-side/in-out. If it does it's toast and most likely the source of your issue. If it seems solid you'll be looking farther up.

Either way, you can check for nasty oily residue at the tailpipe, and raw/unburned oil or coolant will completely **** up O2 sensors and cats.