Back pain? Contractions?

36 weeks tomorrow. Last night and tonight I’ve had like what I can describe extreme pain in my lower back? Kind of feels like contractions in my back but i just don’t know what it is, it’s soo sore tho and it comes and goes in waves My other symptoms are a lot of mucus I’ve been losing everytime I go the toilet, a cold, upset stomach. I know this isn’t labour but is it the start of it? Obviously im still early so just want to know if any ones had similar