Hi Megglevache.
I'm newly pregnant too (BFP on Saturday, TTC chart indicates I'm only 4 weeks at present) and I've also been experiencing cramping type pains and lower back ache. As I can't get an appointment with my GP to either confirm my pregnancy or ask about the cramps until next week, I've been doing a bit of internet researching! It's not unusual to experience cramping pains - as others have said, they could be caused by implantation or yourt ligaments stretching and relaxing. As soon as I started reading about this, I remembered feeling the same way in my previous pregnancies, just at later stages.
I know it's easy for me to say "don't worry" so, if you need some extra reassurance, you could ask your GP or perhaps a community midwife for advice.
Last (but certainly not least) congratulations!!!