Stomachache, cramps, or round ligament pain?

The last 3 nights I’ve had stomach pains before bed. Right now it’s the afternoon and they’re starting. I can’t tell if it’s just a stomach ache, round ligament pains, or cramping (which wouldn’t be good, I’m 21 weeks pregnant.) How can I tell the difference? This is my second pregnancy so I should know but I don’t so 🤷🏼‍♀️ any input is appreciated.