how to time contractions

So i know i’m having contractions.. i’m 36 weeks and 4 days. I’m having menstrual cramping constantly, and have been for about a week. And my doctors tell me my pain i am experiencing are contractions and braxton hicks. But i don’t even really notice a sudden jolt of pain or anything. It’s usually like “oh wow okay i’m hurting again” Will i know for sure when to time them? like will it be a sudden ache where i’m going to be able to tell right away? or will it be like it is right now where i just kind of notice it