I can understand your concern.
Since when have you started noticing this issue?
You need to have a high protein diet along with lots f fruits and vegetables.
Do pelvic floor muscles strengthening exercises.
Start with lot of foreplay and then proceed to intercourse, don't do intercourse straight away.
Take intercourse slowly rather than doing fast. When you feel you are about to ejaculate, just pause for a few seconds.
Then start again.
Consult a general physician in person if issue still persists.
Dr. Anil Kumar Jain.