36 weeks!!!

So this is my 3 pregnancy. Yeah I should know by now warning signs. However, today I began to have these cramps in my stomach that u get them after running lasted for three hours. It was hurting my stomach. No bleeding no mucus plug. With my two boys I always had back labor but this time it’s so different. I don’t know what this is. It was bad enough that I wanted to cry but not bad enough for me to go to hospital. This time I’m pregnant with a girl. Can anyone tell me why is this. Now fours later my back is hurting low.