If you're concerned you have completely evacuated your bowels after a movement, there's a tendency to strain to remove what you believe are stool remaining. You indicate you strain and believe there is something blocking. Don't try so hard and things should improve.
It's unlikely you have "anything" left after your bowel movement. What you are feeling isn't unusual. Sometimes an internal hemorrhoid can give the same sensation. Straining harder can make the sensation worse.
I am sorry you are going through all of this. Unfortunately, unless your physicians can diagnose what this "lump" in your bowel is, they cannot prescribe a treatment for you and things are likely to get worse. The doctors are not rude nor worthless; it just sounds like their hands are tied since there is no diagnosis for what is happening to you.
You need to sit down and talk with your family about what is happening to you. They should be your main support system if these medical problems cannot be dealt with.
It would benefit you to make an appointment with a Gastroenterologist to discuss these symptoms with them.
Likely whatever you are concerned about is far more worrisome than what is actually happening to you. I mean, it sounds as if you've already just about diagnosed yourself with cancer and you've not even gotten tested for these symptoms.
Stop "googling" and pick up the phone and make an appointment.