Hi Chandni, Welcome to HealthcareMagic Forum.
It is absolutely normal for the semen to come out of vagina immediately after your Husband withdraws the penis. The average volume of semen produced at ejaculation is 2 to 5ml and 1 ml would be enough to get you Pregnant. The normal size of Non pregnant uterus
weighs around 40 to 55gms as a result it cannot accommodate much of liquefied semen as a result it throws it out. So there is nothing to get concerned about. So keep trying it. If you do want to stop it, you can use a Tampon and place it inside your vagina immediately after withdrawal.
Wish you Good Health and Good Luck. Take Care.