How do i know if i am in labour?

i am currently 36 weeks pregnant, i had a midwife appointment last tuesday and was told im not engaged but i am starting to feel very tight down there with alot of pressure. I constantly feel like i am leaking even though there is nothing there. About two weeks ago i was told that my plug has broken but i dont understand how if i am not engaged. I am starting to feel cramping very bad which started at about 10pm last night..... could i be in labour?