Got my veneers 2 weeks ago and feel gaps in tooth from the back side? (Photo)

What your feeling looks like a space where the veneer should have fit to, or at least where the cement would fill in. You can have done composite fill in this area, but that won't last long term. Ideally, the veneer or veneers would need to be replaced. Talk to your dentist about it. 

Based upon your enclosed photos, these "gaps" you describe and show do not seem that serious to me.  There is often a temporary period of getting used to the shape of the veneers, especially where they join/meet the tooth on the "tongue" side.  Filling this with composite is a mistake as far as I am concerned, and remaking the veneers for this purpose seems drastic.   As far as the sensitivity to hot and cold, this may not be from this particular issue. I urge you to have a thorough and honest conversation with your cosmetic dentist and hopefully this may be resolved.   It may just be a matter of time to get used to the feel of your new veneers.

Steven M. Goldy, DDS