What Causes Spotting Between Periods?

Since i had my 2nd child by c-section i have spotted inbetween each period (about a year). I took oxyelite pro for 1 1/2 months and it completely stopped. Since i got off the pill it started again. I dont use any form of contreceptives. I didnt know whether something in the pills was helping me or if drinking alot of water with the pills helped? Since i stopped i havent drank much.