Sometimes, belly button along with vaginal walls, buttocks, thighs, anus, can be affected by genital herpes vesicles as uncommon sites for this infection.
Within a few days, vesicles rupture, leaving behind shallow blisters that may ooze or bleed.
After three or four days, scabs form, and the vesicles fall off, healing by themselves without a treatment.
The foul smell may indicate a bacterial superinfection (infection added to the previous one)

Best wishes!
Marija