Anyone know if this could be the start of labour? I’m 36 weeks

For the past 2 days I’ve have really bad diarrhoea, along with constant lower back ache and period like cramps/aching. Could this be the start of labour? Haven’t felt this before? At my midwife appointment last Thursday she said baby’s head was 3/5 engaged and that labour could be near, just didn’t expect it to be this soon. Anyone experienced this before their labour started?