His lack of contact with other people./pets during the cold weather might have made him fearful. It is also possible that he does not feel that you are the pack leader and he feels the need to protect you.
Cesar Milan (The Dog Whisperer) addresses this issue. In fact it is the cause of most dog behavuior issues.
You can watch him on The national Geographic Channel. or get his Books and DVD's from
www.theDogchannel.com