Because your anatomy is a little different, well, the same, but affected differently, it's hard to say if it's normal or not. If you have so much pain that you can't bear the thought of a check up, would they perform a hysterectomy on you to relieve the pain?
If you've had it since the birth, I wouldn't think of cancer. It wouldn't hurt to get checked by your Dr., and if the lump is readily visible that your husband can see it, it can at least be checked initially with minimal pain.
My brother spent his life in a wheelchair, as he had spina bifida. I know that he had many lumps and swelling below the waistline from the pressure caused by sitting all the time. I would go to the Dr. anyway just to talk about pain management, and to see what they can do to help you with pain. You shouldn't have to live with it, if there are options to relieve it. I wish you lots of luck!
If an exam is so painful that you haven't been willing to go, I would ask the nurse to get the doctor to telephone you, and explain exactly that, and ask if he can prescribe a single-dose painkiller that you can take right before the exam.
This may be far fetched, but could it be your cervix? I mean, sitting all the time maybe it's pushed down Hmm, and is it like that all the time or only at arousal?