Maybe you ate something bad?
The day before I went into labor I was vomiting and had diarrhea all day. I was 36 weeks and a ftm and hadn't been sick my whole pregnancy so I thought I had the stomach flu or food poisoning. The next morning my water broke and when I went to L&D my obgyn said I wasn't sick my body was just getting ready for labor. So maybe you're going into labor maybe not lol. Ftms usually go past their due date, my situation was unusual, so most likely it's just late pregnancy symptoms but it's possible you could be going into labor.
They do say your body clears itself out before labour, keep an eye on the cramps and call your midwife just to let her know :)