Okay on the whole overstocked thing.... inches of fish is a very inaccurate way to calculate available space in your aquarium. For example lets look at these 2 1" fish: The dwarf puffer, who has a very high bioload and needs about 3-5g to itself and the endlers livebearer, who has a very low bioload and only needs about .25-.5g per fish.
So stocking according to how long the fish is is not a very accurate way of thinking. In order to more accurately check whether you are ovestocked and how you can fix it, I recommend you plug your tank stats into aqadvisor.com.
Now about the fish: you will really want to make a post in the disease section. There is absolutely NO way even the most experienced fish keepers can give you a 100% certain diagnosis without knowing your ammonia, nitrite, nitrate and pH levels, knowing your tank maintenance schedule and seeing a picture.
We're not fish psychics... when you give us little to no background information we can't give you a straightforward yes-or-no answer.