Could be protein. Could also be glycerin or other humectants (especially if it's been worse with the cold). Could be some other ingredient that your hair just doesn't like. People are very quick to blame protein for any problems they have with their hair, but there are a number of ingredients that can cause problems for some people (some polyquats, aloe, just to name a few).
A couple of ideas for tangles: sealing with oil after applying LI, being very conscious of necklines and fabrics (I love turtlenecks in the winter but they're awful for causing tangles in my underlayer)
To test ingredient sensitivity you just need to read labels and try avoiding each ingredient one at a time to narrow down what's causing the problems.

Modified CG since 11/5/11
CLEANSE: CJ Daily Fix, DevaCare No-Poo, CHS Treatment Shampoo
RO: SS Caitlin's Conditioner, CJ Beauticurls Strengthening
LI: SS Repairing Protein Treatment, CHS Silk Leave-In
STYLE: Re:Coil, Curl Keeper, Deva Ultra Defining Gel, Curls Rock Amplifier,Sweet Curls Elixirs Okra Gel and Hard Hold Gel, SS Curl Enhancing Jelly and Firm Hold Gel