Heavy period like cramps

Hi everyone- I'm at roughly 3 weeks 5 days pregnant and ever since yesterday I've had constant dull lower back ache and as well as in front exactly like a very heavy period would feel. There's been no bleeding yet but I did notice I don't have to pee as much today yet the last few days I was going every 15 mins and I also don't feel as nauseous anymore. 😔 has anyone else experienced this and it been fine?
I'm really worried- my doctors clinic is closed today so I'll have to wait till tomorrow.