Felt sick recently

I took a plan B pill Wednesday around 9 AM and started feeling pretty darn naseous later that day. That led to me not eating much since then, as no food seems appetizing and sometimes gross smelling. I've also been having some constipation problems which is strange for not eating a lot of food. Now after I eat, my stomach starts to hurt for a while until I get up and move around a bit. Are these all just side effects of the pill? Any advice to ease constipation?