Asexuality does exist and is commonly defined as not experiencing sexual attraction to anyone; male, female or otherwise (note I specifically said "sexual"- an asexual can still desire emotional/romantic relationships). While it is possible for asexuality to result in someone who does not enjoy intercourse from a disgust or pain point of view (some asexuals do enjoy it or are indifferent to it, it's a personal thing), I do agree with bb that you need to explore either physical or mental issues in your case, even if you do identify with asexuality, as there is obviously more going on and especially if you want to continue having intercourse with your husband.

Good luck.