When i went for my 6 week check up after giving birth i was reminded to book a smear. Im sure that you can have a smear as soon as your lochia has stopped
I was supposed to have my smear at the 6 week check up after birth too, but I chickened out, I reasoned I'd been 'fiddled' with enough down there at the time!
I was told to wait until 12 weeks as a lot of tests had been coming back with problem results when there wasn't a problem & they were just too early done. I was also told the best time was 8-18 days after the 1st day of your period.