why is birth control a sin? well what was God's first commandment in Genesis - "Be fruitful and multiply". there you go brothers and sisters out there. if you are married why use contraception. If you are using contraception (birth control) you are breaking the will of God (His commandment) and that is a sin.
think about it, why would God make a commandement like that. He obviously wants us Christians to raise Godly children.
Now dont believe in the over population myth, its a lie from the goverments - there are a few satanic reasons for this over population myth. but mostly as to the fact that satan wants us humans to disobey the will of God in every aspect possible. there is plenty of livable land out there and the so called global warming myth is actually just the sun increasing energy output. even then many dispute that the earths temperature is heating up.
do not fear finances or anything like that. Jesus reassures us that we must seek first the kingdom of God and everything else will be added. God will take care of your needs. That is if you are in His will. if you follow the will of God, He will look after you no matter what. believe me it works, God does provide for christian married couples who have many children.
Ultimately if you are married and dont want kids, there is something wrong. why would you deny what God intended you to do (reproduce). its a selfish thing to avoid children. if your holding off kids so you can have a career, more money, overseas holiday trips there is something wrong and you should think what God wants and what His plan is. im not saying every christian should have multiple children, but atleast the majority should try. heck, some should not have any at all, but this applies to a minority of Christians who are called to other things.
so dont be afraid, there are no excuses, and it is a sin to 'close the womb'( birth control). be free to have six, seven, ten, twelve or so kids. its such a blessing to raise Godly children into this world. God Bless