Hello Thanks for query . Loss of libido with low semen volume can not be due to wearing tight undergarments . Desire for sex (Libido) is governed by many factors important being 1) Level of Testosterone in blood 2) Psychological status of an individual 3) An major illness like Diabetes ,hypertension etc Consult qualified urologist for clinical examination and get following basic blood tests done to establish cause for your ED. 1) Haemogram 2) Serum testosterone ( free and Total) 3) Thyroid hormone assessment 4)Blood sugar to rule out diabetes Following measure will help you to boost up your confidence and getting good erection and increase semen volume 1) Practice regular exercise for 45 minutes followed by meditation for 1/2 an hour in the morning. 2) Take high protein diet rich in vegetables and fruits and Vitamin A,C,D,E.and Zinc 3)Take anti oxidants like Almonds 5-6 everyday 4) Avoid alcohol and smoking. Further treatment will depend upon result of these tests and final diagnosis. Dr.Patil..