It takes a while for your period to get back to normal, especially if you are nursing. Also, 2 bc's in 4 months is quite a hormone change in and of itself. I would find one bc and stick to it for a while, or go bc free. Your hormones are already out of whack, so it may be better for you to stay off bc for a bit.
It can take up to a full 12 months before your body goes back to being "normal" hormonally again. Personally my daughter is about to be one in March and my body is no where near normal. I will go for months without a period and then I'll bleed for a full month. If there are too many concerns you should consult your doctor.
imo its probably the birth control. almost all of them have side affects on your period. so with that plus that you just had a baby it will probably take some time for you body to go back to normal. if you are on the pill maybe try a lower dosage, usually if you talk to your doctor they can work with you to find out what is causing it and how you can even it all out