The first thing I would have checked is the oil pan gasket - they can break down over time, especially when you do not put a lot of miles on the car. What you want to do is have the oil pan dropped and check the seal for any damage or evidence of degradation. If you do not see anything immediately visible, I would consider replacing it if the price isn't too unreasonable as a basic first step. But while you are there, have them check for cracks in the pan and lower block where the pan mates with the engine - it isn't likely, but it shouldn't be discounted.
If you do change the pan gasket out and keep having issues, you likely have a leak somewhere else - have someone put UV dye in the oil [link|https://www.amazon.com/Interdynamics-Certified-Fuel-Systems-Ounce/dp/B002M4G24U/|like this|new_window=true] and check back with a [link|https://www.amazon.com/Lichamp-Detector-Automotive-Detection-Protective/dp/B0B43333G5/r|UV flashlight like this|new_window=true] to see where it is coming from. But based on how you described it it is likely the oil pan gasket or something with the pan.