That is why we switched to the 55-lb 6hp , even my wife can pull it at the dock .
Sounds like stray current getting to you , the zinc guppy works well , ground it to the motor . Most outboards don't have enough protection zinc wise .
If you have enough zinc , it goes before the aluminum , if the aluminum is going then you need more zinc or change it several times a year. 50% deterioration of the zinc and it is time to change it .
My neighbor left his Nissan 8hp in salt water for 1 year and had no loss of aluminum and very little zinc loss , of course he was on a mooring about 200yds from the nearest electric . That shoud have ate it up .