If I have a typical virus How Long Am I Contagious For?

Hello,

I realize that this seems like a very lame question, but under the circumstances that I am in, I feel that is is something important to ask.

Here is my situation:

My girlfriend's sister (Who is about 27) has a very premature baby last year that was in the hospital for a very long time after it was born. The baby is home now and is doing very well. But her sister is now VERY concerned with people being sick around the baby because the risk of the baby getting sick (which could be very serious for it). Well, my girlfriend moved out to live with her sister for about 4 months and I am set to visit them on the 29th of this month. But today, I began having a sore throat and I am afraid that I may be coming down with a cold or something like that. I realize that 12 or so days is enough time to rid myself of the symptoms but I really need to know if I am ok in the long run and when I get there. So my question is: If I have a typical virus (cold, sore throat, etc.) how long am I typically contagious for?

I really hope for an answer soon. Thank you for taking the time to read this.