Did my smoking contribute to the my child dying of sids?

Impossible to say. Statistically, sids deaths are more common both in babies born to mothers who smoked during pregnancy, and in babies who are exposed to second hand smoke. But statistics only relate to hundreds or thousands of people; there is no way to know what the cause is in a single case. What is important for you is to quit smoking for your own health, and to have grief counseling for your terrible loss.
Uncertain. By definition, sids deaths are unexplained, meaning no other diagnosis or cause was found. Several factors are known to increase the risk of sids, such as tummy sleeping, co-sleeping and smoking.