Hi, IKH.
Search the Internet for information on "levator ani" and also "proctalgia fugux" to see if the symptoms match yours. It could be swelling from hemmoroids or an anal fissure, which is very painful. Have you tried a sitz basin? Sitting in very warm water can help heal internal injuries by bringing blood circulation to the area. It is very soothing. A hot bath works just the same, although a sitz basin is convenient because it saves stripping down and sitting in a big tub of water. You can find a sitz basin in medical supply stores, or on amazon.