The recurring dark marks are likely a fungal infection. Creams like the one you used often contain steroids, which temporarily suppress inflammation but actually allow the fungus to grow deeper, causing it to return when you stop. To cure this permanently, you should stop using that cream. You need a dedicated, steroid-free antifungal ointment (such as clotrimazole, luliconazole, or terbinafine) and potentially oral antifungal tablets prescribed by a doctor. Please consult a dermatologist for a proper diagnosis and prescription. Meanwhile, keep the area clean and dry, wear loose cotton clothing, and avoid scratching to prevent further spread.