If you want a doctor to answer you need to post in the expert forum.
First of all, we are not doctors on this forum. We're just simple citizens. This warning is shown on the sidebar of the website you are viewing, scroll down and look to the left.
Secondly, there are a couple things you can do. The first thing you can do is have more sex. Experience leads to longer lasting times. Another alternative is to use a toy like the Fleshlight and use it often enough to start lasting longer. Again, it's all about "practice". And do not force yourself to stop going, just let it come naturally.
Last, average sex time is around 4-7 minutes, so do not feel bad if it does not increase by much.