1990 Chevy Cheyenne USING OIL

Engine Mechanical problem
1990 Chevy Cheyenne 6 cyl Two Wheel Drive Automatic

LAST WEEK I CHANGED OIL IN MY PICKUP 4.3L AND TODAY I NOTICED MY OIL GAUGE WAS FLUCTUATING AND ENGINE PINGING I CHECKED OIL AND NOTHING ON DIPSTICK. I FOUND NO OBVIOUS OIL LEAKS AND NO OIL IN RADIATOR. I PUT OIL BACK IN ENGINE AND REVVED UP ENGINE AND HELD HAND AT END OF THE EXHAUST AND LOTS OF WATER AND WHAT LOOKED LIKE OIL WAS ON MY HAND BUT IT DINT FEEL LIKE OIL. IT SMOKED A LITTLE BLUEISH WHITE AT START UP BUT WENT AWAY WHEN ENGINE WARMED UP. WHATS WRONG? WHERE DID MY OIL GO? I PUT MAYBE 200 MILES ON DURING THAT WEEK.