The flickering oil light and overheating - did they start at the same time?
Once, I did an oil and filter change and after that I had no oil pressure. Investigation went as far as dropping the sump to check the pickup wasn't blocked, running flushing oil and all sorts. Couldn't get the oil pump to prime at all then a friend asked about the filter, said put the old one back on, so dived in the bin and fished it out - hey presto instant oil pressure. The point here is an iffy filter could be an issue.
Once I had the oil light come on, had been out laning and then caned it home. had to stop at some traffic lights, oil light flickered at idle. Next morning seemed O.K. but then in the evening when I drove home oil light came on and stayed on - that was a sticky pressure relief valve.
The only way to have any certainty about oil pressure is to check with a gauge. According to the workshop manual - remove the oil pressure switch, fit test gauge. Get engine to normal operating temperature and run up at 2400 rpm, oil pressure should be 1.76kg/cm2 (25psi) so don't be expecting big pressure. The manual says if there is no pressure, check for an air lock. If the pressure is low, overhaul the oil pump.