Have you stuck your finger down into the soil to test moisture level? Does the pot drain quickly when you water? Hoyas are epiphytic; they live in trees, without pots or potting soil. Whatever the medium in your pot, it needs to drain freely and dry quickly. If the potting soil was free draining enough, you could water a hoya daily without any dire consequences - mine are.
They need bright light but not direct sun.
Never fertilize a sick plant unless you see positive signs of nutrient deficiency. Your plant is not suffering from nutrient deficiency. Fertilizer is a stressful for plants. If they don't feel well, its even worse for them (think of having a huge Thanksgiving dinner while suffering from the flu).
