My 10 week old baby has a poo every 4-6days and when she goes she really struggles and cries as if shes in a lot of pain. also her poo is dark green in color and paste texture. is this normal? should i be concerned? she is mostly formula fed.

Dark green bile is the main color agent of poop. Time & action of gut bacteria would eventually change it through lighter greens/yellows/browns. Young infants have flabby/weak belly muscles & often must use their breathing/fussing muscle to push digestion along/poop. They are not necessarily in pain. Some struggle more than others. It usually fades as the muscles strengthen.