You don’t need tools to injure your dick.. Your hands totally suffice ;)
Anyways, without pictures or a more detailed description it could be any number of things.
In general:
I measure healthiness of my dick by the usual “Physiological Indicators”.
During the exercises: If it’s painful (even the least) it can’t be good. And take a step back.. Maybe do some very light jelqs if possible without pain. Or if no-do, I’m going for an erection (better: orgasm without ejaculation) with as less actually touching my unit as possible.
I suppose you try the same in the future ;)
About the vein:
Well, if there’s a hard vein and some fluid build up somewhere at the “start” of where the vein becomes visible this _sounds_ like the vein can’t let go off the blood for whatever reason there may be (and yeah, thus the region that the vein is getting its blood from is filled with more blood than regularly, too).
I don’t think it’s too harmful if you don’t feel any pain _and_ your dick doesn’t feel cold or have an unhealthy color.
I would go see a doctor about it though.. Just in case there’s something more problematic.
After all, there must be a reason why the vein can’t transport the blood away like it used to do.
Take a step back from your PE exercises (stop doing them for the moment) and let it heal.
And go see a doctor (urologist) about it to make sure you don't kill the only dick you will ever have ;)
Ys
P.S: And yeah, if you get a vein to not fully transport the blood away by doing the exercises you are SERIOUSLY overdoing them.