Pregnancy psin. Is that why i'm in pain?

Hi. I'm 2 weeks and a 5 days pregnant counting from ovulation. I am 4 days late on my period. From my last period I'm 4 weeks and 4 days pregnant (I keep very good track of my body). For the a little over a week I've been cramping, I tested positive 3 days before my missed period and the lines were both very dark. I keep reading about round ligaments pain, but I'm not sure if it's too soon for that. The pain can be very painful and I have to roll up just to tolerate it. The cramps are worse then any period cramps I've had. Should I worry about the pain? Am I pregnant with multiples, is that why I'm in pain? I'm not bleeding so I don't think I'm miscarriaging and the psin isn't constant it's on and off. Thanks for your time.