1991 Rover 2 Series Oil Pressure

Hi, I'm thank ful to Dave for his reply last week and I did carry out his instruction, I replaced the engine oil with very high grade and the filter, the oil pressure switch I've already replaced. I went for a 20 mile drive straight away and the oil light didn't flicker-I thought, 'great!' And I thought we'd cracked it. Unfortunately the next day I went for a 2 mile drive, the oil light went off after I'd started the engine, which was fine but towards the end of the 2 miles the oil light came on again and continued to flicker on and off but mostly on til I stopped. The next day 2 mile drive and no oil light. Please, what's going on? Is it the oil pump and engine packing up after only 91000 miles? My garage doesn't have an oil pressure guage, should I try to get that checked, and what if it reads normal, what if it reads low? The engine makes no rattles or bangs and has plenty of poke, it doesn't smoke. Is it the end?Please help.