The clear sap may/may not be a problem as orchids and other plants often exude a sugary sap to attract pollinators. But the yellowing, mushy stem is indicative that something went wrong. From the photo, there looks to be some white spots. They look too small to be mealybug (which is a common pest) or perhaps secondary fungus, or even just a reflection. The flowering stem should be cut off just below the part that is yellow and soft as side shoots should appear since it is early in the season. The wilted leaves can be due to over- or under-watering. You indicated that you might have over-watered. I suggest you knock it out of the container and see if there are any rotten roots. That aside - you are doing correct by watering only when dry and then some.