It is really unfortunate that you have a pain in the groin that is really making you uncomfortable. However, you should seek immediate medication, so that the doctor can advise you on whether to continue playing soccer or not.
Assuming you're healthy. Stretching before and after should help. If you're just starting and playing 3 days a week you should expect some discomfort. If pain persist and does not lessen consult your doctor
Stop a pulled groin is a big deal ! If you keep playin on it it will only get worse. Even to the point of a of a tear in that area do ice heat rest. By the way bro I played football when hurt at 32 yrs old got hurt and I'm done 4 life! At 41 it's pills and very limited action on the field. Love of the game GOD, Family, football is how I like to think about life.(REST)