Timing contractions

How do you time back contractions for the past few days my back has been hurting a lot off and on and sometimes itll hurt for a long while and sometimes ill get the pelvis stretching feeling but mostly only when I walk it seems very hard to time these. My ob said im 1 1/2 cm dialated i told her i wasnt really having contractions but i read something and i never thought that they could mostly be in my back..