Hard Lump under the skin

got this lump about a month now, it feels very solid and I have the impression thats its part of a vein. While in erection/semi erection, it’s very easy to notice/feel while having my grip on it.

Doesn’t heart, can’t squeeze it as it just ‘trembles’ around when pressured.

no pumps/enlargement toys used.

.

any ideas?

I am also presuming you use no ‘natural’ or manual methods of penile enlargement.
Things like this can often only be put down to penile imperfections, they can occur from time to time - so enlargement issues aside, if your penis is erect of some considerable time, or you engage in rough or sustained periods of sex or masturbation then things like this are more likely to occur.
As long as this is not further irritated than it will most likely fade in time - obviously monitor it every few months for any developments in case it is a growth of some kind …