Should having an erection hurt?
No. When discomfort or pain accompanies an erection, it means something is wrong.
A simple cause of aching felt in the gentials is when you have an erection for too long of a period of time. Erections are caused by blood being held in the penis under pressure, but after a period of time, the blood cells run out of oxygen and it causes discomfort or even pain. Generally an erection that lasts longer than an hour will be uncomfortable. An erection that lasts longer than three hours will be painful. Erections lasting more than three hours can cause damage to the body. An increasing cause of erections being held too long is teenagers taking medication meant to treat erectial dysfunction in older men. Teenage boys rarely have problems getting an erection -- if anything, they have problems with too many erections. But adding a medication that increases the probability of having an erection and they might find themselves unable to stop.
If you are uncircumcised, the most common cause of pain is when the foreskin is stuck to the glans at the end of the penis. Normally the foreskin separates in the first few years of life, though for some boys it doesn't happen until just before puberty. Others never learned to rinse under the foreskin while bathing and thus over the years accumulated smegma (oils and dead skin cells) essentially "glue" the foreskin back onto the glans.
In either case, the simplest first step is to grasp your foreskin and stretch it away from your body. You will be surprised how far it will stretch. Do it every chance you can: while changing clothes, using the toilet, or bathing. Only pull as far as is comfortable. Don't pull so far that it hurts. The stretching will cause a shearing action that will gently separate the foreskin from the glans.
Each time you bathe, pull the foreskin back toward your body to unsheathe the end of your penis and expose the glans. Only pull back as far as is comfortable. If you pull too far you might tear the glans or foreskin if they are still stuck. Gently rinse the exposed area of any smegma that you see. Avoid using soap, but if you do get soap on the exposed area, make sure you rinse it very well. Eventually you will be able to completely pull your foreskin back to expose the entire glans. At this point erections will no longer hurt. Just make sure you keep the area under your foreskin clean from now on.
A small percentage of men's foreskins are too tight. The end is restricted so that it squeezes the penis that tries to slide through during an erection. Thus, an erection hurts because the foreskin is being stretched beyond its limits or the squeezing of the penis is cutting off the blood flow to the glans. If this is your problem, use the same technique described above to stretch the skin of the foreskin. Also, grasp the end of the foreskin and pull outwards to stretch the circumference of the opening. If you can, put your fingers inside the opening of the foreskin and gentle stretch it outwards. If this doesn't ease the problem in a month or two, you will need to see a doctor who can ease the problem by making a series of small cuts to the foreskin to loosen the tightness. Occasionally you will find a doctor who doesn't want to bother with the procedure and will recommend a full circumcision. In most cases, circumcision is not necessary. You might want to get a few more opinions if your doctor insists on circumcision.
An even rarer disorder is where the foreskin on the underside of the penis, near the glans is physically too small. When this is the case, an erect penis makes a sharp curve downwards as the tight skin pulls it down. The stretched skin hurts. Again, see a doctor who can perform a minor surgery to detach the foreskin at the bottom from the upper foreskin. As before, circumcision isn't usually necessary to overcome this problem.
Another problem can be cause by blockages inside the chambers of the penis. Usually when this happens, the penis will make a sharp curve in the direction of where the blockage is during an erection. Most of the time it doesn't hurt, but it is possible for the blockage to cause pain during an erection. Often the blockage will dissolve by itself in three to six months. If not, you will need to see a doctor to have the blockage surgically removed.
Finally, you could have pain because of an infection on the skin of the penis. An erection stretches the skin and irritates the infected areas. The irritated areas will be red and raw looking. You will need to see a doctor for medicines to cure the infection.