Hi, I Am A 21 Year Old Male. Recently I've

Hi, I am a 21 year old male. Recently I've been unable to get erection or maintain it while trying to have sex. I'm new at this, thought i've done it twice before. There was no problem like this before but recently i think nothing turns me on. Foreplay or any intimate incident seems to fail. I eat a lot of meat, exercise 5 time a week. What can i do to undo this? This is a very disappointing situation for me.