i can GUARANTEE that you have low oil pressure! i wouldnt drive the car like this at all! i get worried when my cab gets to 15 Psi of oil pressure!
There are a coupple of major possibilities...
1 the oil gallery/picup pipe is clogged with swarf.
2 the main bearings/big ends are fudged
3 there is an oil leak somewhere in the preasurised system (would be fairly noticeable!
4 the oil pump is knackered