During foreplay with my husband, I noticed a lump in the shaft of his penis. the underneath...not on the top part. so we examined it while erect and soft. It is seemingly about the size of : [ ] <---that big. I was thinking maybe it was a swollen vein so we examined it furthur to find that it was more prominant while he was erect....however still able to find it while soft. What could this be???

please let me know if you know what this might be. I realize a doctors visit is in order. it has been a week now, and it is still there...

thanks a mill