You need to lower you poundage if you cant pull it back. I dont care how cold it is you should be able to pull you bow back while hunting.

Also,(you may be doing this already) make sure you keep up your practice shooting during the season. Many people practice all summer and work up to a poundage theyre are proficient with and then stop shooting during the season. Your muscles get weaker and come december/cold weather they cant pull the same weight anymore.