I think psychiatrists just mainly prescribe meds, at least where I live, maybe a psychiatrist who is also a therapist/counsellor, or marriage counsellor.

Depression and some antidepressants can cause a lack of desire as well. (You can google 'antidepressants lack of sex drive' and her meds for side effects.)

Has she ever responded positively or with positive behaviour change to the 'badgering'? Or does she go her own way anyway?
I'd suggest stop the badgering and start telling her what you like about her, or what you liked when you first met her etc.
Communication can improve. I recommend reading 'Five languages of love' - for you, touch is important, for her, maybe some other things.

Do you guys have kids or grandkids? Things worth living for (for her, especially, and for you)?

Ecigs aren't completely harmless either, haven't fully researched this yet though.