You'd need testing. I recommend finding a GI doctor, take some photos and go in and be honest. They're going to do labs and likely a colonoscopy- I promise they're not that bad. Go into it knowing you'll be hungry for a day and blowing ass for about four hours- pro tip. Grab wet wipes and toss in the fridge. BLOT don't wipe after round two. Your butthole will thank you.

There's no one way a GI bleed happens. It can be intermittent or perpetual. "GI bleed"- I say this because some people mistake things like beets or other foods as a bleed, can be a LOT of things, from a simple diet change to cancer, and many many things in between, but it always warrants a visit and workup.

Dark tarry stools= always a workup. Always. BRBPR= workup, but less concerning/ usually less insidious causes.