labor? second baby.. help!

I had my bloody show + mucus plug come out this morning. When this happened with my son, early labor started pretty quick and he was born quickly. So quickly, that my OB requested I call when contractions are 10 minutes apart this time, not 5. 

So. Since 6am, I've been having contractions. They were consistently 8-10 minutes apart, a minute each for an hour 'n a half this morning. I was all set to call my OB and prepping my husband to get home from work.. Then they stopped. So I never called. They started up about an hour later, but they aren't as consistent. Some are 5 minutes apart, some are 10, some last a minute, some are only 30 seconds. And these do not take my breath away. They hurt, and radiate to my lower back, but they aren't how they were with my first.

I know I should call and I probably will.. I just really don't want to call the sitter in and my husband home from work for a false alarm! Any advice? Ps - I'll be 38 weeks tomorrow. My first was 4 days early.