Your wife is very wrong to withhold sex from you. It sounds like you are compatible in every other area and - correct me if I am wrong - you used to be compatible sexually. She may be in a vicious downward spiral due to not receiving the benefit of semen exposure, which would increase her sex drive and decrease her feelings of malaise.
What if you said to her that you needed to have sex with her (and with no artificial contraception - just NFP if necessary) and that she didn't have to enjoy it but she had to submit to it? Would she go along with it out of a sense of duty? I know this is wildly unattractive to men, but sometimes we have to do things for our spouse's benefit, you know? If she started regularly having sex and getting that cocktail of hormones, it is possible - not guaranteed but possible - that this could help.
Of course, she might not consent to this and because marital rape (itself a logical fallacy) is illegal, you cannot do anything about that. Now I personally believe that marital "rape" laws should be repealed for just this reason - sometimes women need what they (think they) do not want. Marital "rape" (which is not really a thing, even if the law says it is) is actually for the benefit of women, not for the lust of men (I am speaking of normal marriages and normal men here, not that very small percentage of men who truly are evil). This is my personal opinion and IS NOT ADVICE. No one reading here should "rape" their wife - that is illegal and will land you in jail, even if you are doing it for her benefit.]