Dear doc, my penis is going soft in 5min time and therefore I am haveing trouble penetrating, it is frustrating for my partner as well.?

You have ED. This is the classic presentation of erectile dysfunction. What you describe, early loss of erection with difficulty or inability to penetrate and maintain penetration, suggests an issue with blood flow. If this is a new problem, it's best you be evaluated for medical causes for your symptoms. You can have your partner come with you to help defuse the frustration and provide education for them.
Trouble relating? Several questions and thoughts come to mind. It may be a psychological vs medical problem. Are you stressed? How long have you and your partner been involved? Is there a performance anxiety because of problems in the relationship or is it the relationship so new it causes anxiety? If you smoke/ engage in illicit drugs, this could cause flaccidity as well. Are you diabetic? Call your pcp to address.