It could be a fibroid. I have one on the outside of my uterus, and, depending on where it sat, it could be felt from the outside. Because it is on a thin stalk, when it moves it can hurt.
I wasn't aware of it at all utnil my first pg. My ob-gyn was surprised to see it on the scan, because she said that she would have felt such a lump had it been present at my most recent exam less than a year prevsouly. So she was fairly certain it had been tiny at the time and was growing due to the pregnancy.
It certainly did grow very big, and moved about a lot. The movement sometimes caused me pain. But no problems during pg or labour. I had it investigated between pregnancies, and decided to leave it be for the time being. It was quite benign, harmless, just uncomfortable. At one point it may have been the cause of heavy periods.
I'm glad I left it alone, because, although it grew again during the next pg, it shrank afterwards and settled into a position where it doesn't move or cause me any problems. Periods became lighter again as well. So no need for surgical intervention. I just live with a Space Invader in my pelvis - I know it's there, but it doesn't bother me.
Hope this reasures you a bit. Try to put it out of your mind and enjoy the holiday. There are so many harmless or non-dangerous things it could be, and all far more likely than the big C-word.
BTW, at 46 you are very likely to have at least one fibroid, they are common as muck at our age