MRi rarely is able to show the cause of most neurological symptoms, I have tinnitus in right ear, because this usually suggest of a benign tumor, or some other disease, I had an MRI, yet it never showed anything.(I do suspect it was related to my allergies over the years). Did you have MRI of the spine, or the rest of your body? if it just your head it may not be enough.
rectal bleeding, is the blood a streak on the poop or toilet paper, that usually is a sign of minor tear in the ****.U sually the result of lack of fiber or constipation. Another possibility is that what your symptoms is stemming from may not be from brain. Have you been tested for vitamin deficiencies, autoimmune, what blood work have you doine.
Have you been tested for MS, ms lesions come and go, hard to diagnose on an MRI, you should consider other autoimmune disease as well.