Insomnia isn't just not being able to fall asleep, it is things like keep waking up during the night and not being able to reach that state of deep sleep every night. Insomnia is also quite dangerous as it can lead to things like cancer, diabetes and depression, so it is important you get it sorted out quickly so you can go back to that blissful sleep. It often steams from having lots of stress or anxiety which stops you from sleeping.
Before you go to doctors about it there are a few things you can try at home which should be able to help you.
You have to treat it like jet-lag. So if you aren't waking up till about 10 o'clock every morning, you have to try and force yourself to wake up earlier and this should make it easier when it comes to sleeping the next night.
Cut out the amount of caffeine you consume during the day. Caffeine is a common substance in coffee and tea, and is often found in chocolate too.
Finally if you still cant sleep try herbal remedies Valerian root, Passion Flower, Chamomile and Lemon Balm are the most recommended to help you sleep. If you have found that you still can't sleep after trying all of the remedies above then visit your doctor and see what they suggest.