Low sex drive

The past yer I have been experiencing very low sex drive, and it has greatly affected my relationship with my partner. It has been hard to figure out the culprit, I mean I love him, but I'm not sure if I'm sexually attracted to him or is it a health issue (I suffer from hypothyroidism). I mean I haven't even felt horny like I used to before or even the desire to masturbate if he's on long trips. Any ideas?