What Causes Brownish Discharge And Stomach Bloating?

hi was wondering if you could please ,ive had unprotected sex for past 6weeks with my bf i had a period on the 15th sep stopped on the 18th sep..we have sex maybe every other day unprotected.yest 4th sep i bled in brown discharge then early hours of the 5th it was a heavy pink and now late tonite its a lite pink colour my tummys bloated and im fit ive also got cramps like its a period i have a 7 month old baby and a 5 year old also im on the champix stop smoking pill been taking it for 6days but going to stop that for time being any suggestions thanks