Pendrive keeps losing formatting

Got a SanDisk Cruzer Glide 8Gib-2.0(high speed) pendrive that keeps losing the formatting(Fat32). Thought it may be the MBR, so re-built it, but haven't solved problem. Plus, drive originally had 7.45G usage available, now it's showing 7.43...missing 20Mibs, but nothing showing in file/on pendrive? Searched for hidden file/partition but found nothing? Ran sector check and it returned 100%. Got some answers/ideas???
THANX;

Rick