How do I know what cramping is normal at 21 weeks?

I am almost 21 weeks and have been having cramping on and off the last few days, mostly at night.

I have noticed my stomach growing quite a bit the last week so not sure if that’s it.

I have a dull back ache but then also have some sharp pains in my abdomen. They don’t last long but they do hurt! At times it feels hard to stand up straight.

Anyone else having a lot of cramping around 20-21 weeks? Not sure if I need to contact my OB or if it can wait til my appt next week.