Of course, one of the problems could be medication - antidepressants or tranquilizers, but there are additional factors that can seriously decrease her sexual drive.
The problem could be that your wife isn’t aroused by the type of sex you both have.
1) Your aren’t doing to her the things what you really want. By example, maybe you deep inside of you want to have rough sex with her, but in reality you act like nice guy and subconsciously she feels it I know, for most men, it is difficult to act roughly to woman he loves (or is in brand new relationships), but if those are your real sexual desires, you should follow them to have great sex.
2) You are not doing to her the things that she really likes, but at the same time, she is too shy to tell you what she really wants. By example, maybe you are one of those guys who doesn't do cunnilingus, but she is too shy to ask for it. Or she fantasizes about rough sex, but thinks if she will ask for it, then you will perceive her as a w***e.
All these are the first guesses, but in context of above mentioned point Nr.2, I really invite you to deeply analyze the following two your own phrases - "I 'm very much a loving person and touch is my love language. Closeness. Caring..”…….……… “We've has the tough talk where I laid it out and things improved...briefly. They only improve when I get angry. Waiting until I'm angry is such an awful tactic (and I've told her this)”.
If I understand correctly, you are a nice guy, who loves his wife, who respects her etc. And it seems that your main mistake is that you are trying to be romantic also during sex. But “nice sex” usually is synonym to “boring sex”, because all the romantic things must be before and after sex, not during it. Love & sex are two completely different concepts and energies. Unfortunately, due to the massive brainwashing in our culture, many people use both these concepts together, and then wonder why their sexual life is deeply unsatisfying.
The other thing you could do - is to invite your wife to take real sexual initiative in sex – you can both agree that she can do what she really wants and ask from you everything that really arouses her, but you have to promise her that you won’t condemn none of her desires….