Hello, Normally young people like you generally have psychological reasons behind poor erection and premature ejaculation.These psychological reasons could be due to overbusy schedule,working late nights,not getting enough time for rest,lack of sleep,strained relations with your wife or other people surrounding you,guilt if having extramarital relationship etc. However there could be other reasons like diabetes,hypertension,hypercholesteremia etc. Other reasons which could precipitate this can be obesity,over use of alcohol,very sedentary life,dependence on various drugs,heavy smoking etc. Since your symptoms are 3 weeks old,you should not worry much and take care of factors mentioned above like Quitting smoking Moderating alcohol Daily aerobic exercises for 45 minutes a day Eating healthy Doing yoga etc. If your problem doesn t improve,you may consult a doctor for finding a physical cause and treatment. Thanks