As jo929, I would recommend that you go and tell your doctor. It can be something really simple that can be taken care of easily, or it might be something deeper, as therese83 said. Even if everything your life is fine, the chemicals in your brain might be playing up!
Try to do something relaxing before you go to sleep, like take a bath. One of the standard pieces of advice is to get up if you haven't managed to fall asleep after 30 min, so that you don't worry about not sleeping, do something for a while, and then try again.
I hope you get some good sleep soon!
This went on with me from when my baby was 3 months old as well. I kept struggling on for a year. It is a form of postnatal depression. I got really bad after a year + went for treatment, I should have gone sooner. One night I just stopped sleeping and that was that, I had no choice but to go for help. There was not enough serotonin in my brain for me to relax and sleep. I was exactly the same.
I tried all kinds of over the counter sleep, natural, pasiflora etc, nothing helped me. I understand completely.
It could be worrying about the baby, but just to make sure tell your Dr about this. luck jo