Erections happen when a penis gets lots of blood supply. Such erections happen even in sleep and occur in newly born babies too. So erection always DOES NOT mean you are thinking about sex Usually in most people, erection goes down once the sex or masturbation results in a discharge, as the blood flow becomes normalised later. You havent mentioned whether you masturbate or have wet dreams. You havent mentioned how the penis becomes after you masturbate and bring out semen. if it goes down. and then becomes erect, perhaps it is a sex drive which is causing you to have quick erections. Sex is a natural instinct and CANNOT be disregarded. If one tries to bottle it up, it will create a explosive problem. So go with the flow. You must satisfy this new hunger of sex which has started with puberty hormones. Its NORMAL to masturbate. So do it few times a week and see. If it solves your problem, you have achieved a good balance. But if it doesnt, perhaps you must visit a urologist. Because Perhaps persistent erection ( priapism ) could be due to some problem in blood circulation or blood type and its bloos vessels.