Early Pregnancy Cramping is Scary

Today is the first day when I've really been scared. And the first day I've felt a good amount of cramping. Everyone says it's normal, but it feels like the first day of my period, just no bleeding. Which is a good sign. But still, it's been coming and going all day today...and when it's on, I have to go to the bathroom to make sure there's no blood, and cry because I'm scared. It's more on the left side and towards the back, which I'm pretty sure is where the baby is. It's also pinching on my sciatic nerve (I had this issue during my first pregnancy). It seems to be calming down a bit, but it's still scary. Will it feel this way off and on throughout my whole pregnancy. I'm contemplating leaving work early because I feel so crappy, but I don't want anyone to think poorly of leaving early because I feel sick, and especially because I'm pregnant and still have a long ways to go.