Hi thirstyforchrist. I'll give you my two cents....which is basically telling you my own story about my husband.
In 2004 he was diagnosed with Multiple Myeloma (bone marrow cancer). Initially, he complained about back pain. He wouldn't go to the doctor so I finally just made the appointment for him myself. I had to trick him to go but I'm glad I did because that ultimately led to the cancer diagnosis. I don't know what would have happened if we had waited any longer.
I'm not saying your husband has cancer....not saying that at all. My point is that you may have to make an appointment for him especially if the knot changed. My own gut feeling thinks a soft movable knot is just a cyst but if it's giving him headaches, maybe the doc can take the knot out.
Can you trick him into going to the doc? Pretend you're going somewhere else, maybe?