Back pain?

So according to my last period I'm 4 weeks pregnant today (had a blood test to confirm and it was positive) anyway. Today like an hour and a half ago I started having really bad lower back pain. I can still move fine just hurts a little but no bleeding or front cramps. Anyway... I had a miscarriage when I was 16. And my first kid at 19. pregnancy was fine no complications. Took til age 22 almost 23 to even get a positive again. Which is this one. I have been wanting this sooo bad and was sooo excited but now I'm freaking out.... Anyone else have lower back pain at 4 weeks exact? And had a good pregnancy that resulted in birth not anything bad... :(