A general rule of thumb is if its painless, its not cancer, which is always reassuring. I havent seen/heard any exceptions to this, but that doesnt mean its a cast iron rule.
I’d go to the doctor. I had an ever-increasing lump on one of my testicles just over 2 years ago, they sent me for an ultrascan (I think thats what it was called anyway). They told me it wasnt cancer, but also told me they didnt know what it was. Not helpful, and since then, its gone, reppeared, and gone again, not sure why, but I tend to ignore it these days.
But definately go to a doctor, for peace of mind and to be on the safe side. Let us know how it turns out.