Stool

I have noticed over the last couple of days a red tint to my stool. Today, dark and light color with red tint. What do you think.

[boron]

Red tint as red streaks or stool of reddish color?

Hemorrhoids, or eating something red (beet-root)...are most often causes.

Rough wiping, straining.

Then food poisoning (goes with diarrhea), intestinal worms (Possible: mucus, bloating, diarrhea).

Diverticulitis (bloating, diarrhea)

Crohn's disease (usually start in young adults...)

Polyp, or cancer...well, not impossible in your age, but 50+ is a common age for colorectal cancer.

[Tommy4747]

I also notice a little tenderness below bottom of breastbone. When I start to sit up from laying position, same are develops a bubble under skin.

[boron]

A bubble - like bloated (distended) stomach? If yes, the gas is probably collecting in your stomach, what may be a symptom of H. pylori infection. There are few different tests for this. If you're bloated, BE SURE to have this test.

If there are any black parts in the stool, it may be a bleeding from the stomach. Black stool may be also from iron pills or some anti-diarrheal drugs.

I seriously recommend having a stool test for blood (Hemocult), and then follow your primary doctor's instructions.