Aslong as you have no bleeding id say its fine. Just drink as much water as you can and stay rested !. if it continues for more than few hours and gets worse i would call the hospital though
I am also 4 weeks and I asked my doctor yesterday she said she would check for ati also to keep a eye on it of its only on one side and its too painful to walk to go to a e.r because it could mean etopic pregnancy. But the pain has moved around so I would guess its our ligaments stretching in our uterius. But its normal to experience pms like symptoms.
It could just be your uterus expanding, or...when I was 6 weeks I had really bad cramping and went to the doctor. found out it was a uti. so I would definitely get checked to make sure.