Van won't run after oil change

I wasn't having any trouble with the van until I took it for oil change. After change, when I stopped at stop sign, it said "low oil pressure". And van stopped.I got it started and took it back and the station checked it, called a dealer and said they didn't know what it was, it wasn't the oil change. It started, I drove it a few blocks and it stopped and said "low oil pressure". I parked it. Later took it five miles, it stopped on me and wouldn't restart. I had it towed home.
A "mechanic" came out, put in two spark plugs, an air filter and put it on charger for six hours. He came back, took charger, didn't talk to me. My mom called him and he said when he took charger off, it started. When I tried to start it it didn't start, it says no oil pressure. (I guess that is because it wouldn't start so that wouldn't have showed up.