Hi, and thanks for your query on eHealth forum!
Yes, hormonal effect of IUD can cause vaginal numbness, provided the numbness started after the IUD was inserted. Another possibility can be pudendal nerve entrapment causing vaginal numbness and inability to enjoy sex. Sciatica and peripheral neuropathies as seen in diabetes or hypothyroidsm too can cause vaginal numbness. It can also be due to injury to the vagina during sex. Low estrogen too can be a cause.
Since a confirmed diagnosis cannot be given on net please consult your gynecologist to find the cause. Hope this helps. Take care!