cobra and HSA

I was on my spouse's health insurance when he retired in June and went on Medicare, so at that time I went on Cobra.  He had been contributing to his HSA.  Can I continue to contribute to the HSA?  And, if so, can I contribute retroactively back to November and then through the end of this year?    Will this be tax deductible when we file our taxes since I will be contributing after tax money?