While it's pretty normal at this stage, I would make sure your nutrition intake is decent so you have optimal energy levels. In-Liven is brilliant, you get a boost when you start taking it. If you don't want to go down that path, take a multi-B complex and decent multi-vitamin. Supermarket brands are crap, they don't contain much of each vitamin to give you a serious boost.

Exercise will also help give you energy, even if it's just walking with the pram. But there is only so much you can do when you are a new mother suffering from sleep torture!!! You might like to check with your doctor to have a blood test to check your iron levels etc just in case.