This is interesting. Fat actually is the holder of testosterone, so losing fat often increases sex drive by releasing the hormone into your system. It may be, that now that food is not acting as a drug (producing dopamine and pleasure) you may be confronting negative emotions that had been neglected. Losing weight can also make one feel very vulnerable physically. That can really kill the sex drive.
I stopped taking antidepressants 2 months a go and since my sex drive has taken a serious dive - which sucks- and I assume it is because I am in a slightly darker place, and my brain does not feel up to having fun. But the body can be retrained. I would advise some talk therapy, if you can afford it.