Hi, I'd like to help you with your question.
A great place to start is by talking to a therapist. You need to get to the root of why you feel jealous and what causes you to bring it into your marriage. To find a therapist, talk to your doctor about a referral or if you attend church, you can talk with your pastor. You can also search on line at http://www.itsgoodtotalk.org.uk/therapists/ or http://www.bacp.co.uk/.
I think you are right, it most likely started in childhood. Here are some of the more common reasons people develop jealousy:
Problems in prior relationships- if someone you cared about was distrustful, you may have learned that others in your life are also distrustful. The pain and hurt caused by the distrustful person would cause you to feel fearful of trusting others.
If you witnessed your parents being jealous- this would cause you to feel that others cannot be trusted. Also, if one or both of your parents were unfaithful in their relationship, then you would come to understand that that is how people act when they are married.
You were cheated on before- if you had prior relationships in which your partner was unfaithful, then you would react with jealousy and suspicion in your current relationship.
Comparisons- if your parents or other important people in your life compared you to others, you would learn to feel jealous.
If you were abused as a child- then you may have a very low self esteem. This could cause you to feel that you do not deserve a good relationship.
Here are some good books to help you understand more about jealousy:
If This Is Love Why Do I Feel So Insecure? by Carl G Hindy, J. Conrad Schwarz and Archie Brodsky
The Courage To Trust: A Guide To Building Deep And Lasting Relationships by Cynthia L. Wall and Sue Patton Thoele
How to Deal with Jealousy: Overcoming Jealousy and Possessiveness is Vital for a Healthy Marriage or Relationship. Learn How to Control Your Jealousy Now. by Taylor Timms
You can find these on Amazon.com or your local library may have them for you.
I hope this has helped you,