First of all, congratulations on your child - I hope the delivery itself was not too difficult.
I will assume that you are not breast-feeding given the initial resumption of your cycles.  I will also assume that you are not on any form of birth control or I think you would have mentioned that to me.
It is not uncommon after the birth of a child to have irregularity in your cycles related to unpredictability of when you ovulate.  In women who are breast-feeding, or even in cases of being around a crying newborn, there is elevation of a hormone called 
Prolactin.   When this is elevated, cycles can be irregular or non-existant.
In the case of a light brown discharge, this might be related to a small amount of 
breakthrough bleeding related to the irregularity in your cycles.  Here is what i would recommend:
1.  If you have had 
unprotected intercourse at any time since delivery, do a home 
pregnancy test.  If it is positive, then contact your OB/GYN
2.  While I am saying this is normal, if you are concerned about the irregularity, temporarily being on birth control is worth considering for cycle regulation.
I hope this helps and good luck!