It sounds like it is not getting enough light. Repotting once per year after blooms have dropped is a good thing. Use a high quality bark mix for orchids or high quality sphagnum moss. If the flower spike dried out you did exactly the right thing by removing it. So try more light without direct sun and be sure to water only if the mix is dry. No wet feet for most orchids. Good luck
Oncidium, perhaps more accurately the oncidium alliance, are a group of plants from South America that span a wide range of habitats. Inside the oncidium alliance there are a number of genera that hybridize freely to create what we call intergeneric oncidium hybrids. These can come in all sorts of shapes and sizes but are generally characterized by large quantities of small to medium flowers borne on a branched stem that generally forms a Christmas-tree shape. The most commonly identified Oncidium are the yellow “dancing lady” type.
Most orchids are not heavy feeders. Many orchids bloom year after year with no fertilizer at all. During active growth, when new leaves are being produced, you may fertilize every other time you water at half the strength recommended on the fertilizer package. However, it's important to deliver water without fertilizer at least once a month to flush excess fertilizer salts from the bark mix and avoid fertilizer burn to the roots.