When should I go in?

I'm 38 + 4 and I've been having cramps/back pain for about 24 hours and I feel alot of pressure like I have to poop but I dont have to. I know everyone says time the contractions but I don't really know what they feel like.. when I was hooked up to the monitor last week they were shocked I wasnt feeling the contractions on the screen. I have a high pain tolerance and a previous back injury so I kind of ignore pain. But I was 2cm and 50% effaced on Monday at my appointment. The hospital is an hour away so I'm not sure when I should actually go in..