Diarrhea 36 weeks

I’m almost 36 weeks pregnant with baby #3. For the past 2 days I’ve had spotting and diarrhea every couple hours. Also lots of cramping. Last night I had intense back cramps (radiated up and down my back - lasting about 30 to 60 minutes)

My entire pregnancy so far I’ve been having the opposite problem. I doubt it’s something I ate since my husband and I eat the same stuff and he’s fine. I have an OB appointment scheduled for tomorrow morning. Should I be worried that labor is approaching? Should I call my OB or just hold out until tomorrow?