Idles rough and runs jerkily They told me it shows 6 plugs misfiring?

I have an engine light on on my Honda Odyssey. I took to an auto parts place where they checked for me the reason code for the engine light. They told me it shows 6 plugs misfiring. I replaced all 6 plugs and the engine light went off and seemed fine for a while. A few days later the engine light returned and now started to idle rough for a short while after starting. I returned to the auto parts for another reading of the scanner. This time they said it showed all 6 coils were misfiring. I'm not sure how to interpret this. How could all 6 coils go bad. In addition the engine now runs rough for a longer period and pulls back when driving. I left the vehicle down for a while to determine how to proceed. Also I've noticed that my coolant level in the reservoir have dropped a couple time within 3 months. This was 1 prior to all these problems and once after started having these problems. I dont know if this is related but it seems there is a leak but I cannot see a leak on the floor of my garage, so not sure where its leaking out.
Note: If I leave the engine running for a while, the rough idling smoothes out but I have the pull backs and jerking when attempting to drive it.