Period like pains at 21 Weeks

I am 21 weeks pregnant today, FTM with identical twins. I started to have a pain up by my ribs on the right side when I would cough or twist funny. I laid down for a bit and now I am having some very strong period like cramps in my lower stomach and to the side. I can feel the girls moving around A LOT. The pains will get pretty strong, then fade off a tad, then  it hits me again. I have not noticed any bleeding. I have drank plenty of fluids today as well as eaten. Should I be concerned? I'm pretty uncomfortable, i just don't know what is pretty normal in pregnancy, let alone a twin one.