we need a little more information or pictures before we can really help here- where are the seams coming apart? did you press them to one side or open? are the fabrics loosely woven and fraying? is it around the outer edges of a block? where a stay stitch would help? were the blocks hand or machine pieced? if hand pieced- did you knot the ends of your threads and do a few back stitches ever few stitches? if machine pieced did you secure any seam not crossed by another line of stitches?
so many things----give a few details we may be able to help