Tell me how to correctly count contractions? In 01-45 I felt a strong …

Tell me how to correctly count contractions? In 01-45 I felt a strong urge to go to the toilet, big and at the same time my lower back and stomach hurt. Nothing came out, I went back to bed and noticed that after some time my lower back continued to ache. I don't understand what moment exactly starts the contraction so I can count it and what moment it ends because my lower back hurts like every minute.