I noticed that when my penis is almost erect or i want to urinate, it looks like an hourglass, a little tight in the middle, and when i empty my bladder, things return to normal, and also when i get erection, the hourglass shape disappears?

Have you ever had trauma injuring your penis? If there's erectile tissue or penile damage it could account for the deformity you describe. However since there's no deformity with a fully erect penis I doubt significant firm scarring is present. I recommend consulting a urologist who will check you for early peyronie's disease or any other penile deformity.