It sounds as though the cream irritated your skin, and irritation can certainly aggravate hyperpigmentation. Retin-A is more likely to be the culprit than hydroquinone. If I were you, while waiting to see the dermatologist, I would try applying the hydroquinone to one spot, just to see whether it irritates you. If it doesn't, apply it to the whole area until you can see the dermatologist. Pigmentation on the torso is often long-standing and hard to treat. At least some of it may indeed be lasting, though other treatments (such as chemical peels) are at least worth contemplating.