Melasma occurs as a result of an overstimulation of pigmentary cells in the deeper layers of the skin. Hydroquinone works by inhibiting the production of melanin at the cellular level but does little to bleach the skin. Since the pigment takes approximately 120 days to reach the skin surface, a time period of 4 months is necessary to see the results of the hyperpigmentation unless aggressive exfoliation is performed.
I recommend a strict regimen for hydroquinone and topical prescription creams that literally transform the skin and skin complexion. However, time is necessary to see the results.
Before switching to more aggressive treatment modalities, you may consider reexamining your skin program to utilize the full benefits of hydroquinone based therapies.
Further, I typically advise against topical corticosteroids for melasma as their long term use is devastating to the skin.