Symptoms of periods or pregnancy?

me and my husband have been ttc since nov2009.i have a regular cycle of 28 days.but after ttc last two months my cycle was shortened to 26days.we ttc last month almost all the fertile days.this month my periods was due at 4th march,i have been having pain since last week.yeaterday i found a brown spot ,stil now no blood flow and all..very scarce brown spotting seen.had back pain and cramps yeaterday..and feel bloated..whatever i eat nowdays i experiance indigestion and feel like vomiting.could this be my normal periods or is it anything else?usually pain seem to disappear when my periods start..but this time it is stil there..not severe as the usual pain i get while i have periods