Talk to Sexologist on Not Able To Go For Second Round Sex

Hello there dear doctors..i am 25 years old male with normal health physique good metabolism excercises, normal libido ,good erection good amount of semen but the problem is is been a month since i got married and i am not able to go for second round even after 8 hours though a have good erection but as soon we start having sex after 2 minutes my penis loose erection and not able to get hard again even after 20 minutes inside or out side the vagina. can someone guide me please what is the issue and any suggestions or treatment to solution.?