What Causes Blood Tinged Discharge With Dull Pain In The Back?

hi i had a baby 9 months ago and due for another smear laters this year. since i had my daughter my body been up the wall when one month with out a period for 4 monthsn during this 4 month period i had blood tinged discharge. my gp checker my cervics and toke swabs she said my cervices looked health. my swabs can back as i had thrush so my gp treated me for it. gone about a month with regular period no spotting all good sept for this month my symptons are blood tinged discharge on and off dull ach in back on right side just above bum somtime on right please help