P0304 cyl 4 misfire & P0303 3 cyl misfire?

Hello, As of this past Sunday, my car has been running weird, not holding it's idle, constantly conking out at lights, engine light on ect. I recently had my car diagnosed and it showed I had a couple cylinder misfires, so I bought platinum spark plugs, and a new coil. Had them installed and still my car is not holding it's idle, conking out, and I am back to square one. I went for another diagnostic and it reads. P0300 Random, multi misfire detected. P0304 cyl 4 misfire & P0303 3 cyl misfire, now I already replaced the coil and plugs and engine light is off, so what could it be & what do I need to do now? I have a mobile mechanic coming later today but I would like some knowledge of my own.