Help please....confused

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I'm 18 weeks first time mom to be

I've been laying down for maybe two hours and I just started cramping in my lower abdomen not to long ago

I went to the bathroom thinking maybe I had to go

I then cleaned my self

There was no blood or mucous but still cramping and hard to move

I layed down again and it seems it's going away has it happened to anyone?

I had sex last night night it be that?