How to know when to go to the hospital?


I know the 511 rule! I am 40 weeks tomorrow. Lost mucous plug/bloody show last night. Leaking discharge or whatever(not water, went to hospital last night and water was still there and cervix closed) slight cramping last night. Progressed....all day today....lower back and lower stomach cramps off and on. Is this contractions?? How to know when to go