You could be cramping because your uterus is growing and the spotting may very well just be some spotting that a lot of women experience in their first trimester. You definately want to contact your Dr. First thing in the morning that way they can check and see what's going on.
If you were cramping and bleeding heavily, there would be more cause for concern. But, I don't think it's anything serious. You won't know until you see your regular Dr. So make sure you go. Even though more than likely, everything's fine, bleeding is not to be taken lightly.
If it makes you feel any better, 50% of pregnant women will bleed at some time during their first trimester. And 50% of them will go on to have normal, healthy pregnancies. And a lot of women cramp. So don't worry too much because that's not good for you or the baby. It really doesn't sound like anything serious, but like I said... Make sure you call your Dr. First thing in the morning.
Please let us know what happens