Yeah it sounds like an internal bacterial infection. It's called Hemorrhagic Septicemia.
I can tell you what I did to save my Angelfish who had that. I used a medicine called Furan:
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=4827
I dosed them, in a 10G tank, (because the smaller the tank the less meds you need to use) with Furan each night (for 3 nights) and every morning did a 50% water change with fresh dechlorinated water.
After three days of dosing them with Furan and every morning doing 50% water changes, I changed another 50% of the water and then I started the whole process over again.
I did that a total of three treatments.
I also jumped the temp up to 85. And bumped up the salt from 1tsp per Gallon to 3tsp per gallon.
The whole healing process took three weeks.
By then my biological suff was dead, so I did a 100% water change. 50% fresh decholrinated tap water and another 50% from my big 55G tank. And seeded the filter again from one in the 55g tank.
Within two more days all the bleeding was reasorbed by the Angel's body.
Of all the times that I have had fish, that had this disease, this is the first time I was able to find something to cure them.
So good luck and I hope this helps!
*Sends healing vibes*