Jealousy is often a barameter of our own emotional state. When we feel insecure or inadequate, we are hypersensitive to what goes on about us.
I believe you had a baby fairly recently. If you feel anything like I did in that first year or so afterwards, you feel tired, ovewhelmed and you tend to put yourself on the back burner in order to care for your family and home.

You also often have to deal with a post baby body, which doesn't always bounce right back. You don't have time to pamper yourself or do the things that you used to do to feel good about yourself. It's easy to see young beautiful girls as "the enemy", even though you know in your heart of hearts that you have nothing to fear.

You say that you love your husband and that you know he won't cheat. Trust your instincts and don't allow yourself to go down that road. If you continue to harbor these feelings of inadequacy and jealousy, it will eat away at the very structure of your marriage.

It's time to reconnect with your husband. See if family will watch the baby for a date night. Let them take the baby early, so that you have time to get all dolled up and feel attractive and desirable. Don't talk about the baby or home issues that night. Focus on you and your husband. Enjoy yourselves. This is how bonds are reforged and strengthened.

If you feel the connection, you have nothing to worry about. Good luck.