I have a hard lump on the bottom of my penis shaft at the base help?

I already asked a question somewhat similar but not much help. It's very visible and noticable when I'm erect at the bottom about the size of a quarter. On top of that my erections feel constricted and hurt sometimes and my penis is a little thinner now. Another problem is that it's not even visible at all when I'm flaccid and both urologists I saw didn't know and brushed it off as nothing. Would an MRI or ultrasound be beneficial? I don't know what to do! Oh and yes I'm circumcised and done growing (20 years old). No stupid comments