Birth control and how to check pregnancy status

Patient: What is the best and safe method to avoid pregnancy. i have one child and i do not need another child till up to 3-4 year which type precaution we use to avoid pregnancy. now a days my wife feeling that she is pregnant again. i want to clear the pregnancy status at early stage. what should i do for know the doubt.

Symptoms: My wife feeling stomach pain (little) and some discharge (white liquid) come out side