Cramps vs contractions

FTM How do you tell the difference between cramps and contractions? Do they eventually intensify to the point you make no mistake?

I’ve had a dull low back ache/cramp. Mostly on my left side lower abdominal region and lower back on my left side this afternoon. Sometimes in the middle and right side as well.

Feels like period cramps, or bowel movements cramps and they’re kind of constant vs coming and going.

38 weeks tomorrow.