Why would my car "throw a spark plug? Twice,not same one

What is your question?

My car threw a spark plug & luckily a gentleman stopped to help me & got it running, then it threw a different plug & l had it fixed, but it threw it again. Now it's running hot & l am told it needs a water pump. I don't drive it often & l seem to recall, that l had a water pump replaced about 2 yrs ago. I put about 50 miles a month on it

What makes this problem better or worse?

I ca drive it about 3 miles before it starts running hot.

How long has your 2000 Mazda 626 had this problem?

About a month but l paid a mechanic for a diagnosis & he says l need a water pump & it's an all day job