Why is my erect penis bent?

Every penis is bit bent and a slight bend upwards is not just normal but desirable.
You may have a problem if your penis is bent to the left or right so much as to make it difficult or even painful to enter your partner during sex.  It could be condition called Peyronie's. This is not an Italian beer. Bent willies are very common and generally do not cause any problem with intercourse. It's a matter of finding what fits, so to speak. If the 'bend' is particularly bad, surgery can improve matters.