Have you always used the same brand and grade of oil?
Penrite, Valvoline are crap. All the second Tier oils are, anything thats from Ozzy is a re-refined oil. Ie, second hand. Eww.
Put a 5w30 Castrol, Mobil, Total or somthing in it. See what happens.
Does the oil smell like fuel at all? Does it seem to use oil after a longish drive and not so much on shorter drives?