If I were you, I would stop trying to self diagnose this issue.
Bite the bullet and take it to a dealer. They will do a compression check and a leak down test to determine the integrity of the engine block and heads.
Also, if they drain the oil, they can tell pretty quickly if there is AF in the oil.
At that point, the issue is down to the two we mentioned.
Why put this off?
If the issue is a head gasket, then you want to fix that right away so as to not ruin the block and pistons etc.
If the block is cracked, that is another story.
Either way, you need a professional diagnosis and you need it fast.
Good luck.
