I think a cold could definitely be a symptom! I read somewhere that before/during implantation, your immune system lowers so that it doesn't try to attack and get rid of the zygote (a foreign invador to your immune system), so I think you would be more susceptible to colds definitely during this time.
Maybe it's just me, but somehow if science is behind it, I feel better haning my hat on it
Good luck and keep us posted!!!
A