Two Weeks After Explant, from Day One Nipples Sensitive and Smell of Stale Milk?

The answer is in your query. As breast tissue contains mild producing glands (lactiferous) any surgery or pressure in this area (especially from within the breast can stimulate them to produce milk. I would not worry as the implants are now removed and the stimulus should also be removed, and the gland tissue should gradually reduce milk production. Just use sterile water to bathe the nipple area until it has stopped secreting.