Once in 2 months, am having severe headache accompanied by right shoulder pain and lower abdomen uneasiness followed by foul smell stool next morning.

Once EVERY 2 months?: I want to make sure I understand that this is happening once EVERY 2 months. For how long does this condition last and what happens after that? Back to normal? I would recommend you get some stool samples and if this is happening every 2 months on a cycle go ahead and consider getting blood work known. You may have an infectious or parasitic type of bowel disease.