Your problem is suggestive of a condition called premature ejaculation. The threshold for ejaculation is short and spontaneous discharge often occurs. Stress, anxiety, other lifestyle associated factors are few important factors to consider before deciding the management. With suitable medications and instructions it can be completely cured.
Next Steps
I would suggest you to consult with a sexologist. For more specific advice on how to get rid of this problem, you can consult me directly here on practo.
Health Tips
It is treatable.