Hi, nightfalls are a healthy phenomenon. They disappear once you enter into regular sexual intercourse. Avoid watching porn content, because the more you watch, the more you are aroused, and the more night falls you get. But, more than that, regular porn watching is not good for a healthy sexual life.
Next Steps
If you are too thin, that is have very lttle fat under your skin, obviously veins show prominently in many places of the body. Eat nutritious food. Get a medical check up to find out any deficiencies causing your underweight.