What Could Cause Tingling Sensation In My Anus Apart From Spasms During Nervousness?

For weeks I ve been experiencing a tingling sensation in my anus. Some times the muscles contract when I become nervous. Almost like a spasm. I ve been to the doctor for a nerve check and did a MRI but nothing came back. Any idea what this is and how I could fix it? Theirs no pain, but it does cause a great deal of anxiety.