“Why is there blood in my eye?”

It may be a broken blood vessel. See an ophthalmologist.

You could have a hemorrhage from a ruptured capillary vessel caused by rubbing the eye too vigorously causing the fragile vessel to rupture sand bleed until the pressure of that blood beneath the thin clear fibrous tissue (Conjunctiva) causes the blood to stop flowing.
It generally goes away within a week, becoming darker red each day, and is innocuous.
You can hasten its disappearance by applying a warm compress for several minutes four times a day. Use a clean wash cloth dipped into warm water, squeeze out drips and apply for 30 seconds. Then dip into the warm to hot water again, squeeze out drips again and reapply for another 30 seconds. Keep that going for five minutes and repeat again 4 times a day.

Roger Ohanesian MD

Subconjunctival hemorrhage is when one or more blood spots appear on the white of your eye. The eye’s conjunctiva contains a lot of tiny blood vessels that can break. If they break, blood leaks between the conjunctiva and sclera. This bleeding is the bright red spot that you see on the white of your eye.

If you have no other bruising, blood in your urine or stool, it is probably of no consequence. Still, it's probably a good idea to have it evaluated by an ophthalmologist to be sure it's not something more severe. See https://www.aao.org/eye-health/diseases/what-is-subconjunctival-hemorrhage

An ophthalmologist is a medical or osteopathic doctor who specializes in eye and vision care. Ophthalmologists complete 12 to 13 years of training and education, and are licensed to practice medicine and surgery. This advanced training allows ophthalmologists to diagnose and treat a wider range of conditions than optometrists and opticians. Typical training includes a four-year college degree followed by at least eight years of additional medical training.

An ophthalmologist diagnoses and treats all eye diseases, performs eye surgery and prescribes and fits eyeglasses and contact lenses to correct vision problems. Many ophthalmologists are also involved in scientific research on the causes and cures for eye diseases and vision disorders. Because they are medical doctors, ophthalmologists can sometimes recognize other health problems that aren't directly related to the eye, and refer those patients to the right medical doctors for treatment. see https://www.aao.org/eye-health/tips-prevention/what-is-ophthalmologist

Could be subconjunctival heme.

Blood shot eye may be due to eye strain, eye rubbing or inflammation or infection. See a doctor.