Really need input

I'm almost 21 weeks with fraternal twins. Last night at about 10:30pm, I laid down on the couch and started to have a pain in my lower left abdomen, under my belly, which I thought was just some normal cramping. However, the pain didn't go on and off like cramps. So I made my way upstairs, thought, "I'll just sleep it off." I woke up this morning and it's still here, which makes it uncomfortable to walk. I don't see my doctor until Friday. Any idea what it could be? How to make it go away?