Are the bricks or stones in your exterior façade bulging out? Is the problem at the top or at the bottom of the wall? In the former case, it’s water seepage; in the latter, it’s a problem with the foundations.
Bulging in walls is often caused by rust at the level of the anchors or deterioration of the mortar and joints as well as the presence of cracks. Whatever the cause, you must take the problem seriously, because a bulging may collapse.