Power issues and coolant leak

Hi, I have the car listed above that over the past three months have had a few issues. My check engine light comes and goes on but it solid on usually. On occasion, it flashes. I can usually restart the car and it just stays on or goes off. I have taken to AutoZone and it says code of cylinder two misfire. I have change the plugs and have had someone look at the wires and the coils and are good. Recently, I have had coolant issues. Two months ago, it overheated and the reserve was low or empty. It was refilled but no leak was detected by the mechanic. No fluid is found on the ground. Today, I check it after a defrost issue and it is dry again. And not any fluid on the ground. So not sure where it is going. I also have noticed a drop in gas mileage. Maybe twenty miles a tank. And also have an rpm problem that comes and goes. Usually around 45 or so, I feel the car almost lose power, then bam it takes off. I have watched the rpm's and they will go from 2,100 to 1,500 then up to 2,800 before settling. Not sure why that is going on. Are all the issues the same issue?