How do I know when menstrual like cramps are contractions?

I’m 31+5 with twins, hoping to make it to 36 weeks. I told my doctor yesterday that I’ve been getting menstrual like aches and pains here and there the last week. She told me to call if I get them within 5 mins of each other because we want to prevent labor this early obviously. The problem I’m having is that they’re prolonged for the most part. It’s not necessarily individual cramps, but more like one for several minutes and then a little later I’ll get the achy feeling for awhile, etc.

How do I know if they’re contractions or just aches and pains of being pregnant? This is my first pregnancy.