Don't Get Periods Without Straining Self Not Taking Iron And Calcium Supplements. Suggestions?

Hi ,I had a C-section and delievered a baby boy on 12 Nov 2011,after which I had periods for 6 weeks.Then when my baby was 9 months old my cycle began and it lasted for 3 days and was normal flow.The next two cycles also were the same.But from the fourth period its been very very scanty and prolonged for days (sometimes there is nothing for a day and the next day it begins ) ,almost 15 days sometimes.What I noticed was if I strained myself physically I started to have a normal flow,This time when I got my periods I purposely swept and mopped my three bedroom house,washed all my clothes and the periods atleast filled up 1/4 of the pad everyday for almost a week.One day in between I did not sweep and mop and there was NO flow through the night.Next day when I strained ,it started off normally.Over all I had periods for a week this month.When I thought it was all over as I was ending up with a clean sanitary napkin,I assumed it was done this month,but again I had a slight flow of say 10 drops day before yesterday and nothing yesterday and again today I have about 10 drops,today I had strained myself and carried my child around when we went for a evening walk.Before my delievery I have never missed a single period ,and almost 99% of the times I have had a 25 day cycle for sure.At that time I used to have back and stomach pains and weakness in legs.But now there is no pain or weakness. I have taken the HPV Vaacine. I am not using any barrier as well. I am still breastfeeding .The only thing that I stopped is taking my iron and calcium supplements .Please give me an advice.Is this normal?