96 Honda civic engine trouble?

I have a 96 Honda Civic. It had a coolant leak on the driver side and I put a radiator stop leak in it.It stopped the leak but now the engine is shaking and it takes 20mins+ for the heat to turn on, if at all. I'm thinking the leak stuff gunked it up but I'm not sure. What could it be. Also I moved from a warmer climate place to a much colder place, could the car just not be used to such cold,especially with it being cold?

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