Well this could be a whole lot of different things. But if you think this is steroid-induced, I'd get your liver checked. Trenbolone, although injectable and skips a pass through the liver, can still wreak havoc on your liver. Especially at such an extreme dose as 700 mg. This can scar the liver and hinder blood flow. As a reaction, veins in the esophagus become dilated and start to bleed; ending in your stool.
This is what happened to me on Tren A @ 560 mg per week. Or it could be hemorrhoids.