I believe the two are interconnected. Did you get a new cap?
Oil changes are rather straightforward to do independently and need little equipment; thus, I would undertake oil changes more regularly, including the oil filter, and likely proceed with one immediately. You may have dislodged debris in suspension that is affecting the oil pressure and level from the last change. Regular alterations will facilitate the elimination of residue.
Owning a historic car enhances satisfaction when the owner actively engages in its maintenance and assumes duties, rather than delegating tasks to technicians. Moreover, there will be an incessant emergence of problems, alongside the financial savings you would accrue. YouTube is an excellent resource, offering several videos that provide detailed instructions on how to do any task related to your specific vehicle. The excitement of a new activity is at your doorstep.
The yellow light is activated by a sensor that monitors oil pressure, while the dipstick gauges the oil level in the sump. These are interconnected but distinct concepts. Allowing the vehicle to remain stationary for many hours will provide an accurate measurement on the dipstick (I presume you own a dipstick, since you were able to assess your oil level in the last discussion).