I just reached 6 weeks myself and have all those things. The cramping and pain you feel is the uterus and muscles stretching and will continue throughout the pregnancy. It would be nice if it were common knowledge because I was freaking out too! Now I kinda get anxious if I DON'T feel a tightness down there lol. If you're not bleeding, no worries. :3
Cramping is normal as longas there's no bleedingand the cramping is unbearable!
However I think you should know there's no way you can avoid miscarriage if it happens it happens.
Cramping and backpain r perfectly normal in early pregnancy so as long as u hve no bleeding u should b fine but it wouldn't hurt to try and take it easy , dnt do too much:-)