Early labour at 37+4?

hello everyone, I'm pregnant with my first baby, so i don't have a clue about signs of labour lol!

im 37+4, my midwife told me at 35wks that baby's head was engaged, and she thinks that I may go early...ive had bad back aches for the past week or so, and today all of a sudden have had very bad nausea, no diarrhea but I am constipated but i have recently been put on iron tablets so it could be that, I've also felt a few twinges like period type pains but nothing unbearable, do you think this could be early labour?or just a dodgy belly lol, thanks everyone