Q: Burining Oil Smell, Car has Oil leak

My car has a small oil leak that needs repair. Due to its increasing age & mileage, on my last oil change on 12/28/2016, I got high-mileage oil for the first time. my car was driving funny and stalled briefly on the way to church. But I restarted it and made it home. When I told my boyfriend, he checked it and told me I was almost out of oil, so he put some of the regular 5w-30 I had in my trunk. We tried to drive it around, and the car started smelling like oil was burning but was not running hot. As I accelerated, it was sluggish and slow. We pulled over, and nothing was burning. We drove it back home and on the way home the same thing happened. My boyfriend said I need to probably take it to my regular mechanic and have my seals looked at and to find out why it's leaking oil, which I'm going to do Tues. But is it possible switching back to the regular oil after putting in high-mileage could have harmed my car & will it be ok? Should I have the oil flushed & replaced w/ high-mileage?

My car has 184000 miles.
My car has an automatic transmission.