Not well perform during sex. Too bad?

Hi I'm 24 old guy first time when I made sex I'm doesn't perform well my sex time is just 5 seconds when I put my penis into vegina I got excited and discharge quickly after this I think it's normal because it's my first time but after doing 4 to 5 time I couldn't perform well just increasing little time 11 seconds my girlfriend doesn't satisfied during this intercourse im asking too many friends and doctors about this problem they told me that you are not physically well so you don't perform well first made your body then you perform my weight is 43 kg and my height is 5.6 inches is this true this is the main cause during sex even I reach climax to quickly.so please help me what the reason behind this unsucess I'm feeling too bad