2001 Blazer running rough

I just bought a 2001 Blazer and it started acting up the day after. I was at a stop and when I pressed the gas pedal nothing was happening, then it was revving up and down until the service engine light came on. I checked the guages and all seemed normal so I looked under the hood for any visual problems, still nothing. I started it and it ran fine the rest of the way home. My friend did a diagnostic test and it came up with 0300 random misfire, and 0150 O2 sensor. It was running fine again and then last night it ran like garbage again, where I would step on the gas and nothing would happen. I felt a clicking when I had my foot on the pedal and it would stop after it registered that it was getting gas, but it eventually died in the middle of an intersection. I drove it home and didn't drive it until today where it ran fine again. I was thinking that it was the fuel pump, but before spending the money for that I wanted to get other opinions.