If you are exclusively breastfeeding (no formula, no solids) and breastfeeding on demand (whenever the baby wants to eat) and do not go longer than 6 hours without breastfeeding, that provides very effective birth control for the first 6 months if you haven't had your period naturally.
It seems you went on birth control right away so it would be hard to know whether you had your period naturally or it was just the lochia.
It can be really frustrating when you get conflicting advice from doctors, especially when it comes to safety. Here is a link to what the Kelly Mom site says about it. It says to avoid estrogen until at least 6 months, partly because it can effect milk supply but does say it is approved for nursing mothers.
http://www.kellymom.com/health/meds/birthcontrol.html
Since the baby is already 3 months, maybe you should just use condoms for a few months until you pass that 6 month stage and then go back on.
Good luck!